[llvm] [AArch64] Avoid expensive getStrictlyReservedRegs calls in isAnyArgRegReserved (PR #190957)

[Benjamin Maxwell via llvm-commits]

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

LGTM, nice speedup! This change makes sense to me given the context of why this check was added for `+reserve-x{1-7}` (see: https://reviews.llvm.org/D48580).

https://github.com/llvm/llvm-project/pull/190957