vfio: Use vfio type1 v2 IOMMU interface

vfio: Use vfio type1 v2 IOMMU interface

The difference between v1 and v2 is fairly subtle, simply more
deterministic behavior for unmaps.  The v1 interface allows the user
to attempt to unmap sub-regions of previous mappings, returning
success with zero size if unable to comply.  This was a reflection of
the underlying IOMMU API.  The v2 interface requires that the user
may only unmap fully contained mappings, ie. an unmap cannot intersect
or bisect a previous mapping, but may cover multiple mappings.  QEMU
never made use of the sub-region v1 support anyway, so we can support
either v1 or v2.  We'll favor v2 since it's newer.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>