aco: improve control flow handling in GFX6-9 NOP pass

aco: improve control flow handling in GFX6-9 NOP pass

Fixes Detroit: Become Human hang. Also affects World of Warships.

pipeline-db (Tahiti):
Totals from affected shaders:
SGPRS: 0 -> 0 (0.00 %)
VGPRS: 0 -> 0 (0.00 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 0 -> 0 (0.00 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 0 -> 0 (0.00 %)

pipeline-db (Polaris):
Totals from affected shaders:
SGPRS: 17168 -> 17168 (0.00 %)
VGPRS: 11296 -> 11296 (0.00 %)
Spilled SGPRs: 1870 -> 1870 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 1472628 -> 1473292 (0.05 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 628 -> 628 (0.00 %)

pipeline-db (Vega):
Totals from affected shaders:
SGPRS: 17168 -> 17168 (0.00 %)
VGPRS: 11296 -> 11296 (0.00 %)
Spilled SGPRs: 1870 -> 1870 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 1409716 -> 1410380 (0.05 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 0 -> 0 (0.00 %)

Max Waves is lower than it should be because of a null winsys bug.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4004>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4004>