rockchip: video: rk_vop: migrate to livetree

This migrates rk_vop (the shared functions used by multiple VOP
mini-drivers) to be compatible with a live tree.

Unfortunately, there's
(i)  a lot of tree traversal needed for a VOP (as each active VOP
     vnode references back to the endpoints in the encoders and vice
     versa) to configure the connection between VOPs and encoders;
(ii) the DTS binding is not too sane and one needs to walk a node's
     parents (the original code just assumed that the device would
     live 3 levels above the property linked through a phandle) until
     a UCLASS_DISPLAY device can be found.

As part of the migration, the code for finding the enclosing display
device has been changed to not assume a specific depth of nesting
(i.e. we walk until we reach the root or find a matching device) and
to use the newly introduced (in the same series) ofnode_get_parent()
function.

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>