tests: mem_protect/mem_map: add data cache manipulations

This adds data cache manipulations, flushing and invalidation,
to the tests where buffer content are being written and
compared. These tests map different virtual pages to the same
physical pages, and write to one of the mapped virtual
addresses. Some SoCs may cache the virtual address separately
and writes to one virtual address will not be reflected to
another virtual address, this failing the comparison. So we
need to manually flush the cache after writing to the buffer,
and invalidating cache before reading. Note that not all reads
and writes need this treatment as some of them only needs to
test for access permissions, and not the memory content.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>