pan/mdg: Limit int64 vectorization

Previously, nir_opt_vectorize was sometimes vectorizing 64-bit
load_const instructions to vec4.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8358>
1 file changed