rockchip: rk3399: move sdram driver to driver/ram

Since we have CONFIG_RAM framwork and its driver folder, move the driver
into it.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

arch/arm/mach-rockchip/rk3399/Makefile

@@ -6,5 +6,4 @@
 
 obj-y += clk_rk3399.o
 obj-y += rk3399.o
-obj-y += sdram_rk3399.o
 obj-y += syscon_rk3399.o

drivers/ram/rockchip/Makefile

@@ -5,3 +5,4 @@
 #
 
 obj-$(CONFIG_ROCKCHIP_RK3368) = dmc-rk3368.o
+obj-$(CONFIG_ROCKCHIP_RK3399) = sdram_rk3399.o