rpi3: Move rng driver to drivers

To allow sharing the driver between the RPi3 and RPi4, move the random
number generator driver into the generic driver directory.

Change-Id: Iae94d7cb22c6bce3af9bff709d76d4caf87b14d1
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/rpi/rpi3/platform.mk b/plat/rpi/rpi3/platform.mk
index b0e7b70..21a880c 100644
--- a/plat/rpi/rpi3/platform.mk
+++ b/plat/rpi/rpi3/platform.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -159,7 +159,7 @@
 endif
 
 ifneq ($(ENABLE_STACK_PROTECTOR), 0)
-PLAT_BL_COMMON_SOURCES	+=	plat/rpi/rpi3/rpi3_rng.c		\
+PLAT_BL_COMMON_SOURCES	+=	drivers/rpi3/rng/rpi3_rng.c		\
 				plat/rpi/rpi3/rpi3_stack_protector.c
 endif