i965/fs: Change SEL and MOV types as needed to propagate source modifiers

i965/fs: Change SEL and MOV types as needed to propagate source modifiers

SEL and MOV instructions, as long as they don't have source modifiers, are
just copying bits around.  This commit adds support to copy propagation to
switch the type of a SEL or MOV instruction as needed so that it can
propagate source modifiers.  This is needed because NIR generates integer
SEL and MOV instructions whenver it doesn't know what else to generate.

shader-db results with NIR:
total FS instructions in shared programs: 4360910 -> 4360186 (-0.02%)
FS instructions in affected programs:     59094 -> 58370 (-1.23%)
helped:                                   341
HURT:                                     0
GAINED:                                   2
LOST:                                     0

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>