cmd/internal/obj/arm: better solution of .S/.P/.U/.W suffix check

cmd/internal/obj/arm: better solution of .S/.P/.U/.W suffix check

Current suffix check is based on instruction, which is not very
accurate. For example, "MOVW.S R1, R2" is valid, but
"MOVW.S $0xaaaaaaaa, R1" and "MOVW.P CPSR, R9" are not.

This patch fixes the above kinds of issues by checking suffix
based on []optab. And also more test cases are added.

fixes #20509

Change-Id: Ibad91be72c78eefa719412a83b4d44370d2202a8
Reviewed-on: https://go-review.googlesource.com/70910
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>