feat(psa): add interface with RSE for retrieving entropy

Add the AP/RSS interface for reading the entropy.  And update the
document for the API.

Change-Id: I61492d6b5d824a01ffeadc92f9d41ca841ba3367
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Icen Zeyada <Icen.Zeyada2@arm.com>
4 files changed