[TableGen] Use some free space in Init to store the opcode for UnOpInit/BinOpInit/TernOpInit allowing those types to be a little smaller. NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256733 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed