iommu/vt-d: Check identity map for hot-added devices

The Intel IOMMU driver will put devices into a static identity
mapped domain during boot if the kernel parameter "iommu=pt" is
used. That means the IOMMU hardware will translate a DMA address
into the same memory address.

Unfortunately, hot-added devices are not subject to this. That
results in some devices not working properly after hot added. A
quick way to reproduce this issue is to boot a system with

    iommu=pt

and, remove then readd the pci device with

    echo 1 > /sys/bus/pci/devices/[pci_source_id]/remove
    echo 1 > /sys/bus/pci/rescan

You will find the identity mapped domain was replaced with a
normal domain.

Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: stable@vger.kernel.org
Reported-by: Jis Ben <jisben@google.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Tested-by: James Dong <xmdong@google.com>
Fixes: 99dcaded ('intel-iommu: Support PCIe hot-plug')
Signed-off-by: Joerg Roedel <jroedel@suse.de>