dt-bindings: msm/mdp: Provide details on MDP interface ports

The MDP4/5 DT node now contains a list of ports that describe how it
connects to external encoder interfaces like DSI and HDMI. These follow
the standard of_graph bindings, and allow us to get rid of the 'connectors'
phandle that contained a list of all the external encoders connected to
MDP.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>