cmd/internal/obj/arm64: fix the wrong sp dst register of ADDS/SUBS instructions

According the armv8-a specification, the destination register of the ADDS/ADDSW/
SUBS/SUBSW instructions can not be RSP, the current implementation does not
check this and encodes this wrong instruction format as a CMN instruction. This
CL adds a check and test cases for this situation.

Change-Id: I92cc2f8e17dbda70f0dce8fddf1ca6d5d7730589
Reviewed-on: https://go-review.googlesource.com/c/go/+/309989


Reviewed-by: eric fang <eric.fang@arm.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Trust: eric fang <eric.fang@arm.com>
Run-TryBot: eric fang <eric.fang@arm.com>
TryBot-Result: Go Bot <gobot@golang.org>