x86: further re-work insn/suffix recognition to also cover MOVSX

x86: further re-work insn/suffix recognition to also cover MOVSX

PR gas/29524

Having templates with a suffix explicitly present has always been
quirky. After prior adjustment all that's left to also eliminate the
anomaly from move-with-sign-extend is to consolidate the insn templates
and to make may_need_pass2() cope (plus extend testsuite coverage).