rockchip: dm: convert fdt_get to dev_read

rockchip: dm: convert fdt_get to dev_read

With the new dev_read functions available, we can convert the rockchip
architecture-specific drivers and common drivers used by these devices
over to the dev_read family of calls.

This covers the DRAM controller initialisation for the RK3188, RK3288
and RK3399... all of these read some of the tuning/setup/timing
parameters from the device-tree.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>