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

[Tom Vijlbrief via llvm-commits]

tomtor wrote:

@benshi001 Hi, can you please have a look? With this and the other PRs `llvm-objdump -d` should disassemble any AVR output without issues. If I have missed an instruction, please let me know.

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