cmd/asm: restore supporting of *1 scaling on ARM64

On ARM64, instruction like "MOVD (R1)(R2*1), R3" is accepted and
assembles correctly with Go 1.16, but errors out on tip with
"arm64 doesn't support scaled register format", since CL 289589.

"MOVD (R1)(R2), R3" is the preferred form. But the *1 form works
before and assembles correctly. Keep supporting it.

Fixes #46766.

Change-Id: I0f7fd71fa87ea698919a936b6c68aa5a91afd486
Reviewed-on: https://go-review.googlesource.com/c/go/+/328229


Trust: Cherry Mui <cherryyz@google.com>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: eric fang <eric.fang@arm.com>