iommupt: Add a kunit test for Generic Page Table

This intends to have high coverage of the page table format functions, it
uses the IOMMU implementation to create a tree which it then walks through
and directly calls the generic page table functions to test them.

It is a good starting point to test a new format header as it is often
able to find typos and inconsistencies much more directly, rather than
with an obscure failure in the iommu implementation.

The tests can be run with 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 --kconfig_add CONFIG_WERROR=n
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.

The format can declare a list of configurations that generate different
configurations the initialize the page table, for instance with different
top levels or other parameters. The kunit will turn these into "params"
which cause each test to run multiple times.

The tests are repeated to run at every table level to check that all the
item encoding formats work.

The following are checked:
 - Basic init works for each configuration
 - The various log2 functions have the expected behavior at the limits
 - pt_compute_best_pgsize() works
 - pt_table_pa() reads back what pt_install_table() writes
 - range.max_vasz_lg2 works properly
 - pt_table_oa_lg2sz() and pt_table_item_lg2sz() use a contiguous
   non-overlapping set of bits from the VA up to the defined max_va
 - pt_possible_sizes() and pt_can_have_leaf() produces a sensible layout
 - pt_item_oa(), pt_entry_oa(), and pt_entry_num_contig_lg2() read back
   what pt_install_leaf_entry() writes
 - pt_clear_entry() works
 - pt_attr_from_entry() reads back what pt_iommu_set_prot() &
   pt_install_leaf_entry() writes
 - pt_entry_set_write_clean(), pt_entry_make_write_dirty(), and
   pt_entry_write_is_dirty() work

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>

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