iommu/vt-d: Update first level super page capability

First-level translation may map input addresses to 4-KByte pages,
2-MByte pages, or 1-GByte pages. Support for 4-KByte pages and
2-Mbyte pages are mandatory for first-level translation. Hardware
support for 1-GByte page is reported through the FL1GP field in
the Capability Register.

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