cmd/asm: add check for register and shift/extension combination on arm64

The current code lacks a check on whether the register and shift/extension
combination is valid, for example the follow instructions also compiles.
	ADD     F1<<1, R1, R3
	ADD     V1<<1, R1, R3
	MOVW    (R9)(F8.SXTW<<2), R19
	VST1    R4.D[1], (R0)

Actually only general registers can perform shift operations, and element
and arrangement extensions are only applicable to vector registers. This
CL adds a check for the register and shift/extension combination on arm64.

Change-Id: I93dd9343e92a66899cba8eaf4e0ac5430e94692b
Reviewed-on: https://go-review.googlesource.com/c/go/+/312571


Trust: eric fang <eric.fang@arm.com>
Reviewed-by: eric fang <eric.fang@arm.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: eric fang <eric.fang@arm.com>
TryBot-Result: Go Bot <gobot@golang.org>