aco: improve get_wait_states()

aco: improve get_wait_states()

pipeline-db (Tahiti):
Totals from affected shaders:
SGPRS: 21208 -> 21208 (0.00 %)
VGPRS: 22388 -> 22388 (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: 3278596 -> 3277004 (-0.05 %) bytes
LDS: 19 -> 19 (0.00 %) blocks
Max Waves: 238 -> 238 (0.00 %)

pipeline-db (Polaris):
Totals from affected shaders:
SGPRS: 64 -> 64 (0.00 %)
VGPRS: 96 -> 96 (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: 5200 -> 5192 (-0.15 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 10 -> 10 (0.00 %)

pipeline-db (Vega):
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 %)

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