SPMD: Add support for SPCI_ID_GET

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 spmc component ID as specified in the manifest
for secure world requests.

Change-Id: Id61725f8195106f9a30d61b9d99ed1d7da8c1163
5 files changed