radv: use scoped barriers

radv: use scoped barriers

fossil-db (LLVM, Navi):
Totals from 843 (0.62% of 135820) affected shaders:
SGPRs: 40456 -> 40480 (+0.06%); split: -0.10%, +0.16%
VGPRs: 39648 -> 39688 (+0.10%); split: -0.01%, +0.11%
CodeSize: 2936164 -> 2932508 (-0.12%); split: -0.21%, +0.09%
MaxWaves: 10828 -> 10827 (-0.01%)

fossil-db changes seem to be due to SPIR-V -> NIR emitting a workgroup
scope shared memory barrier instead of a group_memory_barrier.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5980>