[llvm] [AArch64] Verify ldp/stp alignment stricter (PR #83948)

[Yuta Mukai via llvm-commits]

ytmukai wrote:

I initially intended to solve the assertion failures when the size of MachineMemOperand was unknown (#80841).
However, the alignment verification appeared to be incomplete, so I modified it entirely.
This modification will not actually make a difference because it was not converted consequently under the conditions explicitly excluded by this modification.

@manosanaggh Could you review this patch?

https://github.com/llvm/llvm-project/pull/83948