Based on a 2014-01-13 17:40:58 commit by Julien Grall <email@example.com>
titled "xen/arm64: add xen platform". This is one of many fragments
resulting from that commit.
These are the values appropriate for ARM64 on Xen. Since the ARM64
implementation is more recent, there are fewer changeable settings and
most are constants (unlike x86).
xen_pmap()/xen_unmap() were replaced by VM_MEMATTR_XEN. ARM
specifically needs these mappings cacheable, as such prefer
VM_MEMATTR_WRITE_BACK over VM_MEMATTR_DEFAULT.
Submitted by: Elliott Mitchell <firstname.lastname@example.org>
Original implementation: Julien Grall <email@example.com>, 2021-06-28 15:31:57