rockchip: video: rk3399: enable HDMI output (from the rk_vop) for the RK3399

This commit adds a driver for the RK3399 VOPs capable and all the
necessary plumbing to feed the HDMI encoder. For the VOP-big, this
correctly tracks the ability to feed 10bit RGB data to the encoder.

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