[llvm] [AArch64][BOLT] Document AArch64 optimization flag support (PR #198282)

[Paschalis Mpeis via llvm-commits]

https://github.com/paschalis-mpeis commented:

Hey Amina,

Thanks for your work. I had a quick skim and left a couple of comments.

ccing @aaupov in case he has additional feedback on the structure, etc. We discsused part of this some months ago in 'Office Hours'.

https://github.com/llvm/llvm-project/pull/198282