test(memory share): NWd to SWd device memory sharing

Lend UART2 device memory from the NWd endpoint to an SP.
Check when owning the memory the endpoints write to it.
Also test that the SP cannot access the memory once it
has relinquished ownership.

Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
Change-Id: I24e6a8f97348ee90f043a43921ab08fa1b2b30b3