[llvm] AArch64: Use m_GPtrAdd in selectAddrModeRegisterOffset (PR #217446)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> All of these should have NFC in the titles?
> 
> Otherwise LGTM

I'm increasingly opposed to using NFC tags. They don't really provide much information, and it's misused at least half the time 

https://github.com/llvm/llvm-project/pull/217446