rockchip: rk3308: Add sdram driver

A dm based dram driver for rk3308 u-boot
to get capacity.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/drivers/ram/rockchip/Makefile b/drivers/ram/rockchip/Makefile
index 217366b..c3ec89a 100644
--- a/drivers/ram/rockchip/Makefile
+++ b/drivers/ram/rockchip/Makefile
@@ -9,6 +9,7 @@
 obj-$(CONFIG_ROCKCHIP_RK3188) = sdram_rk3188.o
 obj-$(CONFIG_ROCKCHIP_RK322X) = sdram_rk322x.o
 obj-$(CONFIG_ROCKCHIP_RK3288) = sdram_rk3288.o
+obj-$(CONFIG_ROCKCHIP_RK3308) = sdram_rk3308.o
 obj-$(CONFIG_ROCKCHIP_RK3328) = sdram_rk3328.o sdram_pctl_px30.o sdram_phy_px30.o
 obj-$(CONFIG_ROCKCHIP_RK3399) += sdram_rk3399.o
 obj-$(CONFIG_ROCKCHIP_SDRAM_COMMON) += sdram_common.o