Stop using the DMAP region to map ACPI memory.

On some arm64 boards we need to access memory in ACPI tables that is not
mapped in the DMAP region. To handle this create the needed mappings in
pmap_mapbios in the KVA space.

Submitted by: Michal Stanek (mst@semihalf.com)
Sponsored by: Cavium
Differential Revision: https://reviews.freebsd.org/D15059