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_platform_api.h b/include/lib/psa/rse_platform_api.h
index c9fdb55..fcfeb50 100644
--- a/include/lib/psa/rse_platform_api.h
+++ b/include/lib/psa/rse_platform_api.h
@@ -59,6 +59,18 @@
 psa_status_t
 rse_platform_key_read(enum rse_key_id_builtin_t key, uint8_t *data,
 		size_t data_size, size_t *data_length);
+
+/*
+ * Gets the entropy.
+ *
+ * data		Buffer where the entropy data is to be written.
+ * data_size	Size of the data buffer in bytes.
+ *
+ * PSA_SUCCESS if the entropy is generated successfully. Otherwise,
+ *	it returns a PSA_ERROR.
+ */
+psa_status_t
+rse_platform_get_entropy(uint8_t *data, size_t data_size);
 #endif
 
 #endif /* RSE_PLATFORM_API_H */