intel/compiler: Increase nir_opt_peephole_select threshold

intel/compiler: Increase nir_opt_peephole_select threshold

I tried 2, 4, 6, 8, and 10.  8 seemed to be the sweet spot across all
Intel platforms.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
All Gen7+ platforms had similar results. (Ice Lake shown)
total instructions in shared programs: 14736141 -> 14661140 (-0.51%)
instructions in affected programs: 2272413 -> 2197412 (-3.30%)
helped: 8416
HURT: 140
helped stats (abs) min: 1 max: 1152 x̄: 8.99 x̃: 6
helped stats (rel) min: 0.13% max: 42.55% x̄: 4.15% x̃: 3.20%
HURT stats (abs)   min: 1 max: 140 x̄: 4.73 x̃: 1
HURT stats (rel)   min: 0.03% max: 3.44% x̄: 0.87% x̃: 0.60%
95% mean confidence interval for instructions value: -9.36 -8.17
95% mean confidence interval for instructions %-change: -4.14% -3.99%
Instructions are helped.

total cycles in shared programs: 231560416 -> 228585416 (-1.28%)
cycles in affected programs: 126536021 -> 123561021 (-2.35%)
helped: 7092
HURT: 1898
helped stats (abs) min: 1 max: 419320 x̄: 519.02 x̃: 159
helped stats (rel) min: <.01% max: 77.25% x̄: 13.52% x̃: 11.77%
HURT stats (abs)   min: 1 max: 14518 x̄: 371.91 x̃: 36
HURT stats (rel)   min: <.01% max: 103.23% x̄: 5.92% x̃: 2.55%
95% mean confidence interval for cycles value: -514.34 -147.50
95% mean confidence interval for cycles %-change: -9.69% -9.14%
Cycles are helped.

total spills in shared programs: 5763 -> 5848 (1.47%)
spills in affected programs: 1797 -> 1882 (4.73%)
helped: 13
HURT: 13

total fills in shared programs: 17163 -> 16931 (-1.35%)
fills in affected programs: 7214 -> 6982 (-3.22%)
helped: 22
HURT: 19

total sends in shared programs: 730410 -> 730246 (-0.02%)
sends in affected programs: 2705 -> 2541 (-6.06%)
helped: 114
HURT: 0
helped stats (abs) min: 1 max: 4 x̄: 1.44 x̃: 1
helped stats (rel) min: 0.60% max: 20.00% x̄: 7.26% x̃: 5.88%
95% mean confidence interval for sends value: -1.55 -1.33
95% mean confidence interval for sends %-change: -7.90% -6.62%
Sends are helped.

LOST:   4
GAINED: 0

Sandy Bridge
total instructions in shared programs: 10760511 -> 10724637 (-0.33%)
instructions in affected programs: 961305 -> 925431 (-3.73%)
helped: 3734
HURT: 110
helped stats (abs) min: 1 max: 151 x̄: 9.66 x̃: 8
helped stats (rel) min: 0.14% max: 41.21% x̄: 4.93% x̃: 3.95%
HURT stats (abs)   min: 1 max: 20 x̄: 1.68 x̃: 1
HURT stats (rel)   min: 0.12% max: 5.41% x̄: 0.88% x̃: 0.52%
95% mean confidence interval for instructions value: -9.76 -8.91
95% mean confidence interval for instructions %-change: -4.90% -4.63%
Instructions are helped.

total cycles in shared programs: 153359411 -> 152991077 (-0.24%)
cycles in affected programs: 11615401 -> 11247067 (-3.17%)
helped: 2725
HURT: 1138
helped stats (abs) min: 1 max: 2844 x̄: 164.27 x̃: 80
helped stats (rel) min: 0.02% max: 48.60% x̄: 7.47% x̃: 3.91%
HURT stats (abs)   min: 1 max: 4351 x̄: 69.69 x̃: 25
HURT stats (rel)   min: 0.02% max: 40.00% x̄: 3.39% x̃: 1.47%
95% mean confidence interval for cycles value: -103.18 -87.52
95% mean confidence interval for cycles %-change: -4.57% -3.97%
Cycles are helped.

total sends in shared programs: 584038 -> 583855 (-0.03%)
sends in affected programs: 3512 -> 3329 (-5.21%)
helped: 157
HURT: 0
helped stats (abs) min: 1 max: 5 x̄: 1.17 x̃: 1
helped stats (rel) min: 2.38% max: 25.00% x̄: 6.52% x̃: 6.06%
95% mean confidence interval for sends value: -1.26 -1.07
95% mean confidence interval for sends %-change: -7.17% -5.87%
Sends are helped.

LOST:   23
GAINED: 0

Iron Lake and GM45 had similar results. (Iron Lake shown)
total instructions in shared programs: 8122617 -> 8111592 (-0.14%)
instructions in affected programs: 380503 -> 369478 (-2.90%)
helped: 912
HURT: 86
helped stats (abs) min: 1 max: 129 x̄: 12.19 x̃: 9
helped stats (rel) min: 0.30% max: 39.21% x̄: 3.69% x̃: 2.57%
HURT stats (abs)   min: 1 max: 2 x̄: 1.05 x̃: 1
HURT stats (rel)   min: 0.12% max: 3.64% x̄: 0.54% x̃: 0.36%
95% mean confidence interval for instructions value: -12.00 -10.10
95% mean confidence interval for instructions %-change: -3.56% -3.10%
Instructions are helped.

total cycles in shared programs: 188509780 -> 188534398 (0.01%)
cycles in affected programs: 7211542 -> 7236160 (0.34%)
helped: 859
HURT: 132
helped stats (abs) min: 2 max: 690 x̄: 46.59 x̃: 16
helped stats (rel) min: 0.01% max: 26.76% x̄: 1.53% x̃: 0.33%
HURT stats (abs)   min: 2 max: 1592 x̄: 489.67 x̃: 618
HURT stats (rel)   min: 0.03% max: 185.92% x̄: 23.35% x̃: 6.26%
95% mean confidence interval for cycles value: 9.58 40.10
95% mean confidence interval for cycles %-change: 0.65% 2.93%
Cycles are HURT.