rockchip: rk3568: Add sdram driver

Add the driver for rk3568 u-boot to get sdram capacity.

Signed-off-by: Joseph Chen <chenjh@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 c3ec89a..ca1c289 100644
--- a/drivers/ram/rockchip/Makefile
+++ b/drivers/ram/rockchip/Makefile
@@ -12,4 +12,5 @@
 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_RK3568) += sdram_rk3568.o
 obj-$(CONFIG_ROCKCHIP_SDRAM_COMMON) += sdram_common.o