[llvm] [ARM][AArch64] Split processor and feature definitions out of the ARM.td/AArch64.td [NFC] (PR #88282)

[Jonathan Thackray via llvm-commits]

https://github.com/jthackray approved this pull request.

Makes sense to split them, LGTM.

("git blame" might blame you in the future - would adding this to .git-blame-ignore-revs work?)

https://github.com/llvm/llvm-project/pull/88282