This patch introduces the `SPCI_ID_GET` interface which will return the
ID of the calling SPCI component. Returns 0 for requests from the
non-secure world and the SPCI component ID as specified in the manifest
for secure world requests.

Change-Id: Icf81eb1d0e1d7d5c521571e04972b6e2d356e0d1
Signed-off-by: Max Shvetsov <maksims.svecovs@arm.com>
Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>