i965/fs: Always invert predicate of SEL with swapped arguments

i965/fs: Always invert predicate of SEL with swapped arguments

Commit b616164 added an optimization of b2f generation of a comparison.
It also included an extra optimization of one of the comparison values
is a constant of zero.  The trick was that some value was known to be
zero, so that value could be used in the SEL instruction instead of
potentially loading 0.0 into a register.

This change switched the order of the arguments to the SEL, and, for
some unknown reason, I thought that the predicate should therefore
only be inverted for the == case.  Clearly, it should always be
inverted.

Fixes piglit fs-notEqual-of-expression.shader_test and
fs-equal-of-expression.shader_test.

v2: Don't do the "register already has zero" optimization for the '== 0'
case.  In that case, the register does not have zero when we want to
produce a zero result.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89722
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> [v1]
Tested-by: Lu Hua <huax.lu@intel.com>