ram: px30: add sdram driver

Add the sdram driver for PX30 to support ddr3, ddr4, lpddr2 and lpddr3.

For TPL_BUILD, the driver implement full dram init and without DM
support due to the limit of internal SRAM size.
For SPL and U-Boot proper, it's a simple driver with dm for get
dram_info like other SoCs.

Signed-off-by: YouMin Chen <cym@rock-chips.com>
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/drivers/ram/rockchip/Makefile b/drivers/ram/rockchip/Makefile
index a356369..4bfc3d9 100644
--- a/drivers/ram/rockchip/Makefile
+++ b/drivers/ram/rockchip/Makefile
@@ -3,6 +3,7 @@
 # Copyright (c) 2017 Theobroma Systems Design und Consulting GmbH
 #
 
+obj-$(CONFIG_ROCKCHIP_PX30) += sdram_px30.o sdram_pctl_px30.o sdram_phy_px30.o
 obj-$(CONFIG_ROCKCHIP_RK3368) = dmc-rk3368.o
 obj-$(CONFIG_ROCKCHIP_RK3128) = sdram_rk3128.o
 obj-$(CONFIG_ROCKCHIP_RK3188) = sdram_rk3188.o