iommu/vt-d: Reduce duplicated code to handle virtual machine domains

Reduce duplicated code to handle virtual machine domains, there's no
functionality changes. It also improves code readability.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>

diff --cc drivers/iommu/intel-iommu.c
Simple merge