"LDP (R0), (F0, F1)" and "STP (F1, F2), (R0)" are
silently accepted by the arm64 assembler without
any error message. And this CL fixes that bug.

fixes #26556.

Change-Id: Ib6fae81956deb39a4ffd95e9409acc8dad3ab2d2
Reviewed-on: https://go-review.googlesource.com/125637
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>