iommu/vt-d: Add 256-bit invalidation descriptor support

Intel vt-d spec rev3.0 requires software to use 256-bit
descriptors in invalidation queue. As the spec reads in
section 6.5.2:

Remapping hardware supporting Scalable Mode Translations
(ECAP_REG.SMTS=1) allow software to additionally program
the width of the descriptors (128-bits or 256-bits) that
will be written into the Queue. Software should setup the
Invalidation Queue for 256-bit descriptors before progra-
mming remapping hardware for scalable-mode translation as
128-bit descriptors are treated as invalid descriptors
(see Table 21 in Section 6.5.2.10) in scalable-mode.

This patch adds 256-bit invalidation descriptor support
if the hardware presents scalable mode capability.

Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Sanjay Kumar <sanjay.k.kumar@intel.com>
Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>