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/Kconfig b/drivers/ram/Kconfig
index bb431cc..b454ceb 100644
--- a/drivers/ram/Kconfig
+++ b/drivers/ram/Kconfig
@@ -19,7 +19,7 @@
 
 config TPL_RAM
 	bool "Enable RAM support in TPL"
-	depends on RAM && TPL_DM
+	depends on RAM
 	help
 	  The RAM subsystem adds a small amount of overhead to the image.
 	  If this is acceptable and you have a need to use RAM drivers in