[llvm] [AVR] Add AVR MOVW/ADIW/SUBIW disassembly (PR #146360)

[Tom Vijlbrief via llvm-commits]

tomtor wrote:

The PRs I create are often triggered by issues I encounter when using llvm/rust. I used llvm-objdump on a test program output. Will investigate which instructions are missing with the objdump flag -mcpu

https://github.com/llvm/llvm-project/pull/146360