aco: allow barriers to be skipped during scheduling

aco: allow barriers to be skipped during scheduling

Much better scheduling apparently in 160 shaders

Totals from affected shaders:
SGPRS: 6272 -> 6344 (1.15 %)
VGPRS: 4832 -> 4844 (0.25 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 467192 -> 467428 (0.05 %) bytes
LDS: 459 -> 459 (0.00 %) blocks
Max Waves: 1407 -> 1409 (0.14 %)
SMEM score: 9309.00 -> 11216.00 (20.49 %)
VMEM score: 26679.00 -> 33652.00 (26.14 %)
SMEM clauses: 1817 -> 1776 (-2.26 %)
VMEM clauses: 2286 -> 2288 (0.09 %)
Instructions: 86537 -> 86596 (0.07 %)
Cycles: 676260 -> 676568 (0.05 %)

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/3776>