gallium: Weaken assertion about u_mm's align2 field.

gallium: Weaken assertion about u_mm's align2 field.

vc5 MMU mappings are access-controlled at a 128kb boundary, so the 4kb
here was too small for that purpose.  Allowing any valid align2 value that
u_mm's 32-bit addressing can represent will still catch most cases of
people passing in a byte alignment.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>