iommu/vt-d: Implement reserved region get/put callbacks

This patch registers the [FEE0_0000h - FEF0_000h] 1MB MSI
range as a reserved region and RMRR regions as direct regions.

This will allow to report those reserved regions in the
iommu-group sysfs.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>