[dev.typeparams] cmd/internal/obj/arm64: use ABI-compatible registers in function prologue

Avoid using R1, R2, etc. in function prologue, which may carry
live argument values.

Change-Id: I80322b3f7e8fda7aaff622aaa99bc76d02e09727
Reviewed-on: https://go-review.googlesource.com/c/go/+/322852


Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: David Chase <drchase@google.com>