board: schneider: add RZN1 board support

Add support for Schneider Electric RZ/N1D and RZ/N1S boards, which
are based on the Reneasas RZ/N1 SoC devices.

The intention is to support both boards using a single defconfig, and to
handle the differences at runtime.

Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
diff --git a/drivers/ram/Makefile b/drivers/ram/Makefile
index b281129..6eb1a24 100644
--- a/drivers/ram/Makefile
+++ b/drivers/ram/Makefile
@@ -25,4 +25,5 @@
 endif
 obj-$(CONFIG_ARCH_OCTEON) += octeon/
 
+obj-$(CONFIG_ARCH_RMOBILE) += renesas/
 obj-$(CONFIG_CADENCE_DDR_CTRL) += cadence/