Revert "cmd/internal/obj/arm64, cmd/link: use two instructions rather than three for loads from memory"

This reverts commit 3a9bc571.

Breaks darwin/arm64.

Change-Id: Ib958beacabca48020a6a47332fbdec99d994060b
Reviewed-on: https://go-review.googlesource.com/16906Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>