VT-d: prepare for per-device quarantine page tables (part I)

VT-d: prepare for per-device quarantine page tables (part I)

Arrange for domain ID and page table root to be passed around, the latter in
particular to domain_pgd_maddr() such that taking it from the per-domain
fields can be overridden.

No functional change intended.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>