ac/nir: split 8-bit load/store to global memory on GFX6

Due to possible alignment issues, make sure to split loads/stores
of 8-bit vectors.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4339>
1 file changed