intel/fs: Emit logical-not of operands on Gen8+

intel/fs: Emit logical-not of operands on Gen8+

On Gen8+ specifying negation of a logical operation such as AND actually
performs a logical-not.  Take advantage of this to generate fewer
instructions.

v2: Major rebase.  Use nir_src_as_alu_instr.  Fix swizzle handling.

No changes on any pre-Gen8 platform.

Skylake and Broadwell had similar results. (Broadwell shown)
total instructions in shared programs: 15466902 -> 15466274 (<.01%)
instructions in affected programs: 1262953 -> 1262325 (-0.05%)
helped: 682
HURT: 4
helped stats (abs) min: 1 max: 5 x̄: 1.02 x̃: 1
helped stats (rel) min: 0.03% max: 2.40% x̄: 0.18% x̃: 0.04%
HURT stats (abs)   min: 1 max: 62 x̄: 17.50 x̃: 3
HURT stats (rel)   min: 0.03% max: 1.89% x̄: 0.53% x̃: 0.10%
95% mean confidence interval for instructions value: -1.10 -0.73
95% mean confidence interval for instructions %-change: -0.19% -0.15%
Instructions are helped.

total cycles in shared programs: 410996093 -> 410950440 (-0.01%)
cycles in affected programs: 144389048 -> 144343395 (-0.03%)
helped: 519
HURT: 51
helped stats (abs) min: 1 max: 1060 x̄: 104.46 x̃: 140
helped stats (rel) min: 0.01% max: 10.98% x̄: 0.34% x̃: 0.03%
HURT stats (abs)   min: 1 max: 4060 x̄: 167.90 x̃: 22
HURT stats (rel)   min: <.01% max: 8.20% x̄: 0.96% x̃: 0.25%
95% mean confidence interval for cycles value: -97.16 -63.02
95% mean confidence interval for cycles %-change: -0.32% -0.13%
Cycles are helped.

total spills in shared programs: 95311 -> 95329 (0.02%)
spills in affected programs: 881 -> 899 (2.04%)
helped: 0
HURT: 4

total fills in shared programs: 93629 -> 93634 (<.01%)
fills in affected programs: 794 -> 799 (0.63%)
helped: 1
HURT: 2

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>