iommu/io-pgtable-arm: Add self test for the last page in the IAS

Add a case in the selftests that can detect some bugs with concatenated
page tables, where it maps the biggest supported page size at the end of
the IAS, this test would fail without the previous fix.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
Link: https://lore.kernel.org/r/20241024162516.2005652-3-smostafa@google.com


Signed-off-by: Will Deacon <will@kernel.org>