[llvm] [PowerPC] Add error for incorrect use of memory operands (PR #114277)

[Jake Egan via llvm-commits]

jakeegan wrote:

> Would trying to enforce that the memory operand is the last one work?

There are cases where the memory operand isn't the last one, for example:
https://github.com/llvm/llvm-project/blob/304c41217303ce613de8f4042e570ac6ca8757e8/llvm/test/MC/PowerPC/ppc64-encoding-ISA31.s#L499

I think I could enforce that the memory operand is the second one though.

https://github.com/llvm/llvm-project/pull/114277