anv, nir: Fix using shared memory bools

After we started to use derefs for shared memory in Anv, we are crashing when seeing a shared memory boolean. This happens because neither lower_explicit_io or lower_memory_access_bit_sizes handled bit_size == 1 case properly. Solution proposed is to act as they are effectively 32 bit data -- which is assumed elsewhere and which they will eventually be lowered to.

This MR fixes 024a46a4 ("anv: use derefs for shared memory access") and will also fix an upcoming test in Crucible: crucible!49 (merged).