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>
diff --git a/include/lib/psa/rse_crypto_defs.h b/include/lib/psa/rse_crypto_defs.h
index b94664f..ea1342f 100644
--- a/include/lib/psa/rse_crypto_defs.h
+++ b/include/lib/psa/rse_crypto_defs.h
@@ -11,6 +11,9 @@
 /* Declares types that encode errors, algorithms, key types, policies, etc. */
 #include "psa/crypto_types.h"
 
+/* Value identifying random number generating API */
+#define RSE_CRYPTO_GENERATE_RANDOM_SID		(uint16_t)(0x100)
+
 /*
  * Value identifying export public key function API, used to dispatch the request
  * to the corresponding API implementation in the Crypto service backend.