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>