[SelectionDAG] Add some comments to ISDOpcodes.h about the operands of MLOAD, MSTORE, MGATHER, MSCATTER. NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340898 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed