agx: Align the reg file for 256-bit vectors

agx: Align the reg file for 256-bit vectors

This fixes live range splitting with 3D textureGrad(), which involves vectors
larger than the natural 128-bit maximum and hence requires special handling.
Fixes this assert with a combination of debug flags and new patches:

   unsigned int find_best_region_to_evict(struct ra_ctx *, unsigned int,
   unsigned int *, unsigned int *):
   Assertion `(rctx->bound % size) == 0 && "register file size must be aligned
   to the maximum vector size"' failed

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>