iommu/vt-d: Add set domain DOMAIN_ATTR_NESTING attr

This adds the Intel VT-d specific callback of setting
DOMAIN_ATTR_NESTING domain attribution. It is necessary
to let the VT-d driver know that the domain represents
a virtual machine which requires the IOMMU hardware to
support nested translation mode. Return success if the
IOMMU hardware suports nested mode, otherwise failure.

Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>