[X86] Remove X86ISD::PCMPGTM/PCMPEQM and instead just use X86ISD::PCMPM and...

[X86] Remove X86ISD::PCMPGTM/PCMPEQM and instead just use X86ISD::PCMPM and pattern match the immediate value during isel.

Legalization is still biased to turn LT compares in to GT by swapping operands to avoid needing extra isel patterns to commute.

I'm hoping to remove TESTM/TESTNM next and this should simplify that by making EQ/NE more similar.

llvm-svn: 323604