Prevents assertion failures in func.shader-ballot.basic.q0 and other
tests starting with "nir/algebraic: Optimize some b2f of integer
comparison".
Vector immediates, bfloat, and 8-bit floats are still not supported.
v2: Almost complete re-write based on suggestions from Ken.
v3: Don't retype() on a brw_imm_f value.
Fixes: f8e54d02f7 ("intel/compiler: Relax mixed type restriction for saturating immediates")
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38978>
985ace332b