aco: rework boolean phi pass

aco: rework boolean phi pass

The pass should now create much less linear phis.

Removes piles of phis and lots of sgpr spilling from Detroit: Become
Human and parallel-rdp.

fossil-db (Navi):
Totals from 7654 (5.63% of 135946) affected shaders:
SGPRs: 796224 -> 787616 (-1.08%); split: -1.08%, +0.00%
VGPRs: 576164 -> 572116 (-0.70%); split: -0.70%, +0.00%
SpillSGPRs: 147695 -> 52258 (-64.62%)
SpillVGPRs: 2167 -> 2102 (-3.00%)
CodeSize: 80671680 -> 76240420 (-5.49%); split: -5.50%, +0.01%
Scratch: 137216 -> 135168 (-1.49%)
MaxWaves: 54235 -> 54707 (+0.87%)
Instrs: 15569429 -> 14820569 (-4.81%); split: -4.82%, +0.01%

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Co-authored-by: Daniel Schürmann <daniel@schuermann.dev>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3388>