iommu/vt-d: Copy IR table from old kernel when in kdump mode

When we are booting into a kdump kernel and find IR enabled,
copy over the contents of the previous IR table so that
spurious interrupts will not be target aborted.

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