rockchip: video: rk_hdmi: migrate to livetree

The rk_hdmi (shared functions for multiple HDMI mini-drivers) has been
using devfdt_get_addr() to read the HDMI controller's IO base address.
This will cause a failure with a live tree.

This changes the driver to use dev_read_addr() which is safe both for
flat trees and live trees.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: Klaus Goger <klaus.goger@theobroma-systems.com>
Reviewed-by: Anatolij Gustschin <agust@denx.de>