refactor the Value*/offset pair from MachineMemOperand out to a new

refactor the Value*/offset pair from MachineMemOperand out to a new
MachinePointerInfo struct, no functionality change.

This also adds an assert to MachineMemOperand::MachineMemOperand
that verifies that the Value* is either null or is an IR pointer type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114389 91177308-0d34-0410-b5e6-96231b3b80d8