rockchip: rk3288: 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>
diff --git a/drivers/ram/rockchip/Makefile b/drivers/ram/rockchip/Makefile
index 50b9d51..95aae48 100644
--- a/drivers/ram/rockchip/Makefile
+++ b/drivers/ram/rockchip/Makefile
@@ -6,4 +6,5 @@
 
 obj-$(CONFIG_ROCKCHIP_RK3368) = dmc-rk3368.o
 obj-$(CONFIG_ROCKCHIP_RK3188) = sdram_rk3188.o
+obj-$(CONFIG_ROCKCHIP_RK3288) = sdram_rk3288.o
 obj-$(CONFIG_ROCKCHIP_RK3399) = sdram_rk3399.o