mdss: display: Add writeback support for WFD

- Implement APIs used to support wifi display (WFD) based on ioctls and
  functions declared in linux/msm_mdp.h.
- Restructure writeback interface file to support custom output formats
  and take buffers from WFD APIs.

Change-Id: I3e6b75bd8b7d73eb20c97899de1891bbd85e9fa4
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>