nir: Transform expressions of b2f(a) and b2f(b) to a ^^ b

nir: Transform expressions of b2f(a) and b2f(b) to a ^^ b

All Gen platforms had pretty similar results. (Skylake shown)
total instructions in shared programs: 14276892 -> 14276886 (<.01%)
instructions in affected programs: 484 -> 478 (-1.24%)
helped: 2
HURT: 0

total cycles in shared programs: 532578397 -> 532578395 (<.01%)
cycles in affected programs: 3522 -> 3520 (-0.06%)
helped: 1
HURT: 0

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Thomas Helland <thomashelland90@gmail.com>