rpi3: Introduce hardware RNG driver

Note that this is a non-secure RNG. This is only useful for educational
purposes.

Change-Id: If359c8d0f755ef8e416986de7fbca34679a523e1
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/plat/rpi3/rpi3_private.h b/plat/rpi3/rpi3_private.h
index 9d1744e..91b7add 100644
--- a/plat/rpi3/rpi3_private.h
+++ b/plat/rpi3/rpi3_private.h
@@ -33,6 +33,9 @@
 /* IO storage utility functions */
 void plat_rpi3_io_setup(void);
 
+/* Hardware RNG functions */
+void rpi3_rng_read(void *buf, size_t len);
+
 /* VideoCore firmware commands */
 int rpi3_vc_hardware_get_board_revision(uint32_t *revision);