i965: Use the nir_move_comparisons pass.

i965: Use the nir_move_comparisons pass.

While the below stats are encouraging this pass will also become
very usefull for avoiding regression once
brw_do_channel_expressions() and brw_do_vector_splitting() are
disabled.

On Broadwell:

total instructions in shared programs: 13078787 -> 13060898 (-0.14%)
instructions in affected programs: 1809827 -> 1791938 (-0.99%)
helped: 4527
HURT: 157

total cycles in shared programs: 256562762 -> 256590424 (0.01%)
cycles in affected programs: 159749392 -> 159777054 (0.02%)
helped: 5583
HURT: 2289

total spills in shared programs: 14929 -> 14923 (-0.04%)
spills in affected programs: 62 -> 56 (-9.68%)
helped: 1
HURT: 0

total fills in shared programs: 20144 -> 20141 (-0.01%)
fills in affected programs: 253 -> 250 (-1.19%)
helped: 1
HURT: 3

LOST:   0
GAINED: 2

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>