x/arch/arm64: refine objdump test to avoid false alarm
x/arch/arm64: refine objdump test to avoid false alarm

TestObjdumpARM64* is fuzzy test which randomly generates instructions for
decoder and uses host objdump to compare results. Some old objdump wrongly
decodes ldur*/stur*/prfum as ldr*/str*/prfm. Refine allowedMismatchObjdump
function to allow the mismatches to avoid false alarm.

Fixes golang/go#21486

Change-Id: I8909ca2657bd86ec5287e1ade7b17fe87f4ced22
Reviewed-on: https://go-review.googlesource.com/56810
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Run-TryBot: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/arch,golang/arch