rockchip: rk3188: Add sdram driver

rockchip: rk3188: Add sdram driver

The sdram controller blocks are very similar to the rk3288 in utilizing
memory scheduler, Designware uPCTL and Designware PUBL blocks, only
limited to one bank instead of two.

There are some minimal differences when setting up the ram, so it gets
a separate driver for the rk3188 but reuses the driver structs, as there
is no need to define the same again.

More optimization can happen when the modelling of the controller parts
in the dts actually follow the hardware layout hopefully at some point
in the future.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Kever Yang <kever.yang@rock-chips.com>