arm64: Handle changing self-referential DMAP pages

Support changing the property of a DMAP page that holds it's own page
table entry.

Because we need to perform a break-before-make sequence to change the
properties of pages a page that also holds it's own page table entry
will fault in the make part of the sequence.

Handle this by mapping the page with a temporary mapping as we already
do when demoting a superpage.

Reviewed by: kib
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D55943