[X86] Converge X86ISD::VPERMV3 and X86ISD::VPERMIV3 to a single opcode.

These do the same thing with the first and second sources swapped. They previously came from separate intrinsics that specified different masking behavior. But we can cover that with isel patterns and a single node.

This is a step towards reducing the number of intrinsics needed.

A bunch of tests change because we are now biased to choosing VPERMT over VPERMI when there is nothing to signal that commuting is beneficial.

llvm-svn: 333383