Revert "Revert r339977: [GISel]: Add Opcodes for a few LLVM Intrinsics"

This reverts commit 7debc334e6421bb5251ef8f18e97166dfc7dd787.

I missed updating legalizer-info-validation.mir as I had assertions
turned off in my build and that specific test requires asserts. Fixed it
now.

llvm-svn: 340197