Many instructions can not have a .S suffix, such as MULS, SWI, CLZ,
CMP, STREX and others. And so do .P and .W suffixes. Even wrong
assembly code is generated for some instructions with invalid
suffixes.

This patch tries to simplify .S/.W/.P checks. And a wrong assembly
test for arm is added.

fixes #20377

Change-Id: Iba1c99d9e6b7b16a749b4d93ca2102e17c5822fe
Reviewed-on: https://go-review.googlesource.com/43561Reviewed-by: Cherry Zhang <cherryyz@google.com>