iommupt: Add the basic structure of the iommu implementation

The existing IOMMU page table implementations duplicate all of the working
algorithms for each format. By using the generic page table API a single C
version of the IOMMU algorithms can be created and re-used for all of the
different formats used in the drivers. The implementation will provide a
single C version of the iommu domain operations: iova_to_phys, map, unmap,
and read_and_clear_dirty.

Further, adding new algorithms and techniques becomes easy to do across
the entire fleet of drivers and formats.

The C functions are drop in compatible with the existing iommu_domain_ops
using the IOMMU_PT_DOMAIN_OPS() macro. Each per-format implementation
compilation unit will produce exported symbols following the pattern
pt_iommu_FMT_map_pages() which the macro directly maps to the
iommu_domain_ops members. This avoids the additional function pointer
indirection like io-pgtable has.

The top level struct used by the drivers is pt_iommu_table_FMT. It
contains the other structs to allow container_of() to move between the
driver, iommu page table, generic page table, and generic format layers.

   struct pt_iommu_table_amdv1 {
       struct pt_iommu {
	      struct iommu_domain domain;
       } iommu;
       struct pt_amdv1 {
	      struct pt_common common;
       } amdpt;
   };

The driver is expected to union the pt_iommu_table_FMT with its own
existing domain struct:

   struct driver_domain {
       union {
	       struct iommu_domain domain;
	       struct pt_iommu_table_amdv1 amdv1;
       };
   };
   PT_IOMMU_CHECK_DOMAIN(struct driver_domain, amdv1, domain);

To create an alias to avoid renaming 'domain' in a lot of driver code.

This allows all the layers to access all the necessary functions to
implement their different roles with no change to any of the existing
iommu core code.

Implement the basic starting point: pt_iommu_init(), get_info() and
deinit().

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Tested-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Tested-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

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