nir: Recognize i2b(b2i(x)) as x.

Helps the same set of programs as the previous commit.

instructions in affected programs:     4490 -> 4346 (-3.21%)
helped:                                8

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Glenn Kennard <glenn.kennard@gmail.com>
1 file changed