intel/fs: Allow NOT instructions in conditional discard optimization

intel/fs: Allow NOT instructions in conditional discard optimization

I don't know why I explicitly disallowed NOT in the first place. :(

All Intel platforms had similar results. (Ice Lake shown)
total instructions in shared programs: 14549846 -> 14549770 (<.01%)
instructions in affected programs: 12934 -> 12858 (-0.59%)
helped: 76
HURT: 0
helped stats (abs) min: 1 max: 1 x̄: 1.00 x̃: 1
helped stats (rel) min: 0.13% max: 5.56% x̄: 1.04% x̃: 0.90%
95% mean confidence interval for instructions value: -1.00 -1.00
95% mean confidence interval for instructions %-change: -1.25% -0.84%
Instructions are helped.

total cycles in shared programs: 203793967 -> 203792696 (<.01%)
cycles in affected programs: 77920 -> 76649 (-1.63%)
helped: 67
HURT: 1
helped stats (abs) min: 2 max: 36 x̄: 19.00 x̃: 16
helped stats (rel) min: 0.04% max: 4.68% x̄: 2.35% x̃: 2.28%
HURT stats (abs)   min: 2 max: 2 x̄: 2.00 x̃: 2
HURT stats (rel)   min: 0.03% max: 0.03% x̄: 0.03% x̃: 0.03%
95% mean confidence interval for cycles value: -20.75 -16.63
95% mean confidence interval for cycles %-change: -2.57% -2.05%
Cycles are helped.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3965>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3965>