radv: relax shared alignment requirements in mem_vectorize_callback

radv: relax shared alignment requirements in mem_vectorize_callback

fossil-db (GFX10.3):
Totals from 13 (0.01% of 139391) affected shaders:
CodeSize: 241316 -> 238684 (-1.09%)
Instrs: 42251 -> 41912 (-0.80%); split: -0.81%, +0.01%
Cycles: 1991192 -> 1974668 (-0.83%); split: -0.83%, +0.00%
VMEM: 4067 -> 4102 (+0.86%)
SMEM: 569 -> 578 (+1.58%)
SClause: 848 -> 858 (+1.18%)
Copies: 3077 -> 2992 (-2.76%); split: -3.12%, +0.36%

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/8762>