Use AVX512PIi8 for the alt forms of vcmp instructions. This adds the TB prefix and keeps the mnemonic from starting with an extra 'v'

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192272 91177308-0d34-0410-b5e6-96231b3b80d8
Replace a couple instructions with patterns referring to other instructions with same encoding and operands. Mark a couple other instructions as CodeGenOnly since we have FR and VR instructions and only one of them is needed by the assembler/disassembler.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192274 91177308-0d34-0410-b5e6-96231b3b80d8