drivers: renesas: ddr: Move to common

Move ddr driver code to common directory, so that the same
code can be re-used by both R-Car Gen3 and RZ/G2 platforms.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Change-Id: I9aef73d3e9a027a127ce7483b72d339559866727
diff --git a/drivers/renesas/common/ddr/ddr_b/ddr_b.mk b/drivers/renesas/common/ddr/ddr_b/ddr_b.mk
new file mode 100644
index 0000000..0334780
--- /dev/null
+++ b/drivers/renesas/common/ddr/ddr_b/ddr_b.mk
@@ -0,0 +1,7 @@
+#
+# Copyright (c) 2015-2021, Renesas Electronics Corporation. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+BL2_SOURCES += drivers/renesas/common/ddr/ddr_b/boot_init_dram.c