iommu/amd: Introduce helper function to update 256-bit DTE

iommu/amd: Introduce helper function to update 256-bit DTE

The current implementation does not follow 128-bit write requirement
to update DTE as specified in the AMD I/O Virtualization Techonology
(IOMMU) Specification.

Therefore, modify the struct dev_table_entry to contain union of u128 data
array, and introduce a helper functions update_dte256() to update DTE using
two 128-bit cmpxchg operations to update 256-bit DTE with the modified
structure, and take into account the DTE[V, GV] bits when programming
the DTE to ensure proper order of DTE programming and flushing.

In addition, introduce a per-DTE spin_lock struct dev_data.dte_lock to
provide synchronization when updating the DTE to prevent cmpxchg128
failure.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Suggested-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20241118054937.5203-5-suravee.suthikulpanit@amd.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>