arm: support MSR instruction in the disassembler

Though MRS is correctly disassembled, MSR can not be recognized.
This patch fixes this issue and adds corresponding tests.

Fixes golang/go#20762

Change-Id: I59292f2a267d18cac7c012efaf0727bd9b8d5bb1
Reviewed-on: https://go-review.googlesource.com/48310
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
3 files changed