glsl: only allow 32 bits atomic operations on images

glsl: only allow 32 bits atomic operations on images

EXT_shader_image_load_store says:
   The format of the image unit must be in the "1x32" equivalence class
   otherwise the atomic operation is invalid.

ARB_shader_image_load_store says:
   We will only support 32-bit atomic operations on images

Fixes: fc0a2e5d017 ("glsl: add EXT_shader_image_load_store new image functions")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5688>