iommupt: Add a kunit test for the IOMMU implementation

iommupt: Add a kunit test for the IOMMU implementation

This intends to have high coverage of the page table format functions and
the IOMMU implementation itself, exercising the various corner cases.

The kunit tests can be run in the kunit framework, using commands like:

tools/testing/kunit/kunit.py run --build_dir build_kunit_arm64 --arch arm64 --make_options LLVM=-19 --kunitconfig ./drivers/iommu/generic_pt/.kunitconfig
tools/testing/kunit/kunit.py run --build_dir build_kunit_uml --kunitconfig ./drivers/iommu/generic_pt/.kunitconfig
tools/testing/kunit/kunit.py run --build_dir build_kunit_x86_64 --arch x86_64 --kunitconfig ./drivers/iommu/generic_pt/.kunitconfig
tools/testing/kunit/kunit.py run --build_dir build_kunit_i386 --arch i386 --kunitconfig ./drivers/iommu/generic_pt/.kunitconfig
tools/testing/kunit/kunit.py run --build_dir build_kunit_i386pae --arch i386 --kunitconfig ./drivers/iommu/generic_pt/.kunitconfig --kconfig_add CONFIG_X86_PAE=y

There are several interesting corner cases on the 32 bit platforms that
need checking.

Like the generic tests, these are run on the format's configuration list
using kunit "params". This also checks the core iommu parts of the page
table code as it enters the logic through a mock iommu_domain.

The following are checked:
 - PT_FEAT_DYNAMIC_TOP properly adds levels one by one
 - Every page size can be iommu_map()'d, and mapping creates that size
 - iommu_iova_to_phys() works with every page size
 - Test converting OA -> non present -> OA when the two OAs overlap and
   free table levels
 - Test that unmap stops at holes, unmap doesn't split, and unmap returns
   the right values for partial unmap requests
 - Randomly map/unmap. Checks map with random sizes, that map fails when
   hitting collisions doing nothing, unmap/map with random intersections and
   full unmap of random sizes. Also checks iommu_iova_to_phys() with random
   sizes
 - Check for memory leaks by monitoring NR_SECONDARY_PAGETABLE

Reviewed-by: Kevin Tian <kevin.tian@intel.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>