x86_iommu/amd: Prepare for interrupt remap support

x86_iommu/amd: Prepare for interrupt remap support

Register the interrupt remapping callback and read/write ops for the
amd-iommu-ir memory region.

amd-iommu-ir is set to higher priority to ensure that this region won't
be masked out by other memory regions.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>