[llvm] [M68k] Add remaining addressing modes for Atomic operations (PR #115523)

[John Paul Adrian Glaubitz via llvm-commits]

glaubitz wrote:

@knickish Could you begin the commit summary with a capital letter and maybe replace "remaining" with "missing"? And I think "pic" should be all all-caps, i.e. "PIC" as it's an acronym.

As for the testing goes, I can confirm that this change fixes the remaining LLVM backend errors we have seen so far when building Rust code on M68k which is amazing ;-).

https://github.com/llvm/llvm-project/pull/115523