ANDROID: driver/io-pgtable-arm: Add missing callback in unmap_pages_walk

Currently, unmap_pages_walk calls the unmapped paddr callback for:
- An unmapped page with size equals to pgsize(argument).
- An unmapped page with size equals pgsize, which is part which of
  larger block that was broken.

However, this was missing a third case where table is fully unmapped,
where the table size covers the pgsize (but the actual pages are
smaller).

Bug: 333874255
Bug: 277989609
Bug: 278749606

Change-Id: I76e7ef62084195db6e93310b37a15f7031a40fa8
Signed-off-by: Mostafa Saleh <smostafa@google.com>