cmd/internal/obj/arm64: adjust rule for VMOVQ instruction

The VMOVQ instruction stores a 128-bit number into a V register, for
example:
    VMOVQ $0x1122334455667788, $0x99aabbccddeeff00, V2
From a documentation (https://pkg.go.dev/cmd/internal/obj/arm64) point
of view, the value in V2 should be 0x112233445566778899aabbccddeeff00,
however the value is actually 0x99aabbccddeeff001122334455667788. The
reason is that we misplaced the high 64-bit and the low 64-bit in the
literal pool. To maintain backward compatibility, this CL adjusts the
rule of VMOVQ instruction to make the documentation consistent with the
code.

Fixes #50528

Change-Id: Ib51f59e97c55252ab2a50bbc6ba4d430732a7a04
Reviewed-on: https://go-review.googlesource.com/c/go/+/377055


Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Eric Fang <eric.fang@arm.com>
Run-TryBot: Eric Fang <eric.fang@arm.com>
Trust: Eric Fang <eric.fang@arm.com>
TryBot-Result: Gopher Robot <gobot@golang.org>