iommu/vt-d: Do not re-use domain-ids from the old kernel

Mark all domain-ids we find as reserved, so that there could
be no collision between domains from the previous kernel and
our domains in the IOMMU TLB.

Tested-by: ZhenHua Li <zhen-hual@hp.com>
Tested-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>