iommu/vt-d: Avoid duplicated code for PASID setup

After each setup for PASID entry, related translation caches must be
flushed. We can combine duplicated code into one function which is less
error prone.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>