feat(psa): interface with RSS for NV counters

feat(psa): interface with RSS for NV counters

Adding AP/RSS interface for retrieving and incrementing non-volatile
counters.

The read interface implements the psa_call:
psa_call(RSS_PLATFORM_SERVICE_HANDLE,
         RSS_PLATFORM_API_ID_NV_READ,
         in_vec, 1, out_vec, 1);

where the in_vec indicates which of the 3 counters we want, and the
out_vec stores the counter value we get back from RSS.

The increment interface implements the psa_call:
psa_call(RSS_PLATFORM_SERVICE_HANDLE,
         RSS_PLATFORM_API_ID_NV_INCREMENT,
         in_vec, 1, (psa_outvec *)NULL, 0);

where, again, in_vec indicates the counter to increment, and we don't
get any output parameter from RSS.

Through this service, we will be able to get/increment any of the 3 NV
counters used on a CCA platform:
- NV counter for CCA firmware (BL2, BL31, RMM).
- NV counter for secure firmware.
- NV counter for non-secure firmware.

Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
Signed-off-by: Raef Coles <raef.coles@arm.com>
Change-Id: I4c1c7f4837ebff30de16bb0ce7ecd416b70b1f62