aco: rework barriers and replace can_reorder

fossil-db (Navi):
Totals from 273 (0.21% of 132058) affected shaders:
CodeSize: 937472 -> 936556 (-0.10%)
Instrs: 158874 -> 158648 (-0.14%)
Cycles: 13563516 -> 13562612 (-0.01%)
VMEM: 85246 -> 85244 (-0.00%)
SMEM: 21407 -> 21310 (-0.45%); split: +0.05%, -0.50%
VClause: 9321 -> 9317 (-0.04%)

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/4905>
12 files changed