i965/fs: Allow flipping cond mod for negated arguments.

i965/fs: Allow flipping cond mod for negated arguments.

This allows us to apply the optimization in cases where the CMP's
argument is negated, by flipping the conditional mod. For example, it
allows us to optimize this:

   add(8)       temp   a      b
   cmp.l.f0(8)  null   -temp  0.0

into

   add.g.f0(8)  temp   a      b

total instructions in shared programs: 5958360 -> 5955701 (-0.04%)
instructions in affected programs:     466880 -> 464221 (-0.57%)
GAINED:                                0
LOST:                                  1

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>