broadcom/compiler: increase peephole limit to 24 instructions

broadcom/compiler: increase peephole limit to 24 instructions

This helps by reducing the number of branches with their corresponding
delay slots, at the expense of additional register pressure. It also helps
a lot with SFU stalls, probably because removing control-flow blocks
gives us more QPU scheduling flexibility to hide them.

Shader-db results below correspond to the "closed shaders" set, since the
full set is very dominated by the massive impact this change has on Skia's
shaders (for the better), so this is probably more representative of real
impact:

total instructions in shared programs: 11887255 -> 11854898 (-0.27%)
instructions in affected programs: 538170 -> 505813 (-6.01%)
helped: 1653
HURT: 43
Instructions are helped.

total threads in shared programs: 385924 -> 385872 (-0.01%)
threads in affected programs: 236 -> 184 (-22.03%)
helped: 22
HURT: 48
Inconclusive result (%-change mean confidence interval includes 0).

total uniforms in shared programs: 3552808 -> 3547894 (-0.14%)
uniforms in affected programs: 157486 -> 152572 (-3.12%)
helped: 1673
HURT: 35
Uniforms are helped.

total max-temps in shared programs: 2062403 -> 2064720 (0.11%)
max-temps in affected programs: 18209 -> 20526 (12.72%)
helped: 168
HURT: 369
Max-temps are HURT.

total spills in shared programs: 1937 -> 1994 (2.94%)
spills in affected programs: 79 -> 136 (72.15%)
helped: 0
HURT: 1

total fills in shared programs: 2652 -> 2717 (2.45%)
fills in affected programs: 115 -> 180 (56.52%)
helped: 0
HURT: 1

total sfu-stalls in shared programs: 19349 -> 18010 (-6.92%)
sfu-stalls in affected programs: 2321 -> 982 (-57.69%)
helped: 674
HURT: 74
Sfu-stalls are helped.

total inst-and-stalls in shared programs: 11906604 -> 11872908 (-0.28%)
inst-and-stalls in affected programs: 541339 -> 507643 (-6.22%)
helped: 1656
HURT: 43
Inst-and-stalls are helped.

total nops in shared programs: 245740 -> 238085 (-3.12%)
nops in affected programs: 19282 -> 11627 (-39.70%)
helped: 1335
HURT: 76
Nops are helped.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22922>