rockchip: video: Split out HDMI controller code

Designware HDMI controller and phy are used in other SoCs as well. Split
out platform independent code.

DW HDMI has 8 bit registers but they can be represented as 32 bit
registers as well. Add support to select access mode.

EDID reading code use reading by blocks which is not supported by other
SoCs in general. Make it more general using byte by byte approach, which
is also used in Linux driver.

Finally, not all DW HDMI controllers are accompanied with DW HDMI phy.
Support custom phys by making controller code independent from phy code.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Tested-by: Nickey Yang <nickey.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>