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 <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Eduardo Habkost <[email protected]>
Cc: Marcel Apfelbaum <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Suravee Suthikulpanit <[email protected]>
Reviewed-by: Peter Xu <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>