aco: don't move memory accesses to before control barriers

aco: don't move memory accesses to before control barriers

Fixes random failures of dEQP-VK.image.qualifiers.volatile.cube_array.r32i
and similar tests on Vega.

fossil-db (Navi):
Totals from 6 (0.00% of 135946) affected shaders:
VMEM: 1218 -> 1110 (-8.87%); split: +2.46%, -11.33%
SMEM: 174 -> 189 (+8.62%)
Copies: 84 -> 87 (+3.57%)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Fixes: cd392a10d05 ('radv/aco,aco: use scoped barriers')
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6174>