rockchip: rk3128: add sdram driver

RK3128 support up to 2GB DDR3 sdram, one channel, 32bit data width.

This patch is only used for U-Boot, but not for SPL which will
comes later, maybe after we merge all the common code into a common
file.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/drivers/ram/rockchip/Makefile b/drivers/ram/rockchip/Makefile
index 45b5fe7..1a1e557 100644
--- a/drivers/ram/rockchip/Makefile
+++ b/drivers/ram/rockchip/Makefile
@@ -5,6 +5,7 @@
 #
 
 obj-$(CONFIG_ROCKCHIP_RK3368) = dmc-rk3368.o
+obj-$(CONFIG_ROCKCHIP_RK3128) = sdram_rk3128.o
 obj-$(CONFIG_ROCKCHIP_RK3188) = sdram_rk3188.o
 obj-$(CONFIG_ROCKCHIP_RK322X) = sdram_rk322x.o
 obj-$(CONFIG_ROCKCHIP_RK3288) = sdram_rk3288.o