arm/armasm: fix wrong register order in SMLABT/SMLATB/SMLATT/SMLAD/SMLSD

SMLABT/SMLATB/SMLATT/SMLAD/SMLSD are MLA(mul&add) like instructions,
which need the third register to be the addend. But currently the addend
is placed in the first position in the decoded register list.

This patch fixes it and adds corresponding tests.

Change-Id: I57f3e96876c54497badf1a12ae7dae18fe6fcc11
Reviewed-on: https://go-review.googlesource.com/47890
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
2 files changed