iommu/vt-d: Don't copy translation tables if RTT bit needs to be changed

We can't change the RTT bit when translation is enabled, so
don't copy translation tables when we would change the bit
with our new root entry.

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