iommu/amd: Introduce interrupt remapping ops structure

Currently, IOMMU support two interrupt remapping table entry formats,
32-bit (legacy) and 128-bit (GA). The spec also implies that it might
support additional modes/formats in the future.

So, this patch introduces the new struct amd_irte_ops, which allows
the same code to work with different irte formats by providing hooks
for various operations on an interrupt remapping table entry.

Suggested-by: Joerg Roedel <joro@8bytes.org>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>