arm64 requires either no stack frame or a frame with a size that is 8 mod 16
(adding the saved LR will make it 16-aligned).

The cmd/internal/obj/arm64 has been silently aligning frames, but it led to
a terrible bug when the compiler and obj disagreed on the frame size,
and it's just generally confusing, so we're going to make misaligned frames
an error instead of something that is silently changed.

This CL prepares by updating assembly files.
Note that the changes in this CL are already being done silently by
cmd/internal/obj/arm64, so there is no semantic effect here,
just a clarity effect.

For #9880.

Change-Id: Ibd6928dc5fdcd896c2bacd0291bf26b364591e28
Reviewed-on: https://go-review.googlesource.com/12845Reviewed-by: Austin Clements <austin@google.com>