nir: Fix lowering of bitfield_insert to shifts.

nir: Fix lowering of bitfield_insert to shifts.

The bfi/bfm behavior change replaced the bfi/bfm usage in
lower_bitfield_insert_to_shifts with actual shifts like the name says,
but it failed to handle the offset=0, bits==32 case in the new
lowering.

v2: Use 31 < bits instead of bits == 32, to get the 31 < (iand bits,
    31) -> false optimization.

Fixes regressions in dEQP-GLES31.*bitfield_insert* on freedreno.

Fixes: 165b7f3a4487 ("nir: define behavior of nir_op_bfm and nir_op_u/ibfe according to SM5 spec.")
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>