pan/midgard: Enable RA for st_vary

pan/midgard: Enable RA for st_vary

Now that all the piping is in place to do so without regressions, we
flip on automatic register allocation for varyings. Hooray!

total instructions in shared programs: 4025 -> 3915 (-2.73%)
instructions in affected programs: 1667 -> 1557 (-6.60%)
helped: 62
HURT: 0
helped stats (abs) min: 1 max: 3 x̄: 1.77 x̃: 2
helped stats (rel) min: 0.93% max: 20.00% x̄: 10.80% x̃: 10.64%
95% mean confidence interval for instructions value: -1.89 -1.66
95% mean confidence interval for instructions %-change: -12.50% -9.11%
Instructions are helped.

total bundles in shared programs: 2683 -> 2520 (-6.08%)
bundles in affected programs: 1066 -> 903 (-15.29%)
helped: 62
HURT: 0
helped stats (abs) min: 1 max: 3 x̄: 2.63 x̃: 3
helped stats (rel) min: 2.94% max: 42.86% x̄: 23.85% x̃: 22.50%
95% mean confidence interval for bundles value: -2.83 -2.43
95% mean confidence interval for bundles %-change: -27.73% -19.97%
Bundles are helped.

total quadwords in shared programs: 4192 -> 4027 (-3.94%)
quadwords in affected programs: 1584 -> 1419 (-10.42%)
helped: 62
HURT: 0
helped stats (abs) min: 1 max: 4 x̄: 2.66 x̃: 3
helped stats (rel) min: 1.85% max: 30.00% x̄: 16.49% x̃: 16.52%
95% mean confidence interval for quadwords value: -2.87 -2.46
95% mean confidence interval for quadwords %-change: -19.14% -13.84%
Quadwords are helped.

total registers in shared programs: 433 -> 411 (-5.08%)
registers in affected programs: 67 -> 45 (-32.84%)
helped: 23
HURT: 1
helped stats (abs) min: 1 max: 1 x̄: 1.00 x̃: 1
helped stats (rel) min: 25.00% max: 50.00% x̄: 41.30% x̃: 50.00%
HURT stats (abs)   min: 1 max: 1 x̄: 1.00 x̃: 1
HURT stats (rel)   min: 14.29% max: 14.29% x̄: 14.29% x̃: 14.29%
95% mean confidence interval for registers value: -1.09 -0.74
95% mean confidence interval for registers %-change: -45.45% -32.52%
Registers are helped.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>