amd iommu: properly detach from protection domain on ->remove

Some drivers may use the dma api during ->remove which will
cause a protection domain to get reattached to a device.  Delay the
detach until after the driver is completely unbound.

[ joro: added a little merge helper ]

[ Impact: fix too early device<->domain removal ]

Signed-off-by: Chris Wright <chrisw@redhat.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>