msm: mdss: Add support for multiple WFD writeback modes

Different versions of MDSS hardware have different WFD
blocks such as
1.) Writeback WFD block connected to interface mixer.
2.) Writeback block shared between WFD and rotator.
3.) Dedicated WFD block using the writeback mixer.
We need separate handling for each of these wfd writeback
modes. Add support to take care of this.
Make the necessary changes in the MDSS DT files to support
this for different MDP revisions.

Change-Id: Ib95699bd1d8f720f4f044608850eeed60455d6ed
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>