[dev.typeparams] cmd/compile: enable register args on ARM64

Now it will be used for functions marked go:registerparams.

test/abi tests are passing with it.

Change-Id: I5af37ae6b79a1064832a42c7ef5f2cc0b5b6a342
Reviewed-on: https://go-review.googlesource.com/c/go/+/322854


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