iommu/vt-d: Copy translation tables from old kernel

If we are in a kdump kernel and find translation enabled in
the iommu, try to copy the translation tables from the old
kernel to preserve the mappings until the device driver
takes over.
This supports old and the extended root-entry and
context-table formats.

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