iommu: io-pgtable-arm: Disable tests for 16Kb and 64Kb granules

Our performance improvements are intended to be used with only the 4Kb
granule.  Disable testing with other settings.

Additionally, the unmap path has been modified to support unmapping sizes
which are not exact block or granule sizes in a single function call.
Remove the WARN() from dummy_tlb_add_flush() to avoid false positives for
this case.

Change-Id: Ie4e5bc55bc830122901fce3edd0bade42b409de5
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>