drm/msm/mdp5: Add a CAP for Source Split

drm/msm/mdp5: Add a CAP for Source Split

Some of the newer MDP5 versions support Source Split of SSPPs. It is a
feature that allows us to route the output of a hwpipe to 2 Layer
Mixers. This is required to achieve the following use cases:

- Dual DSI: For high res DSI panels (such as 2560x1600 etc), a single
  DSI interface doesn't have the bandwidth to drive the required pixel
  clock. We use 2 DSI interfaces to drive the left and right halves
  of the panel (i.e, 1280x1600 each). The MDP5 pipeline here would look
  like:

         LM0 -- DSPP0 -- INTF1 -- DSI1
        /
hwpipe--
        \
         LM1 -- DSPP1 -- INTF2 -- DSI2

  A single hwpipe is used to scan out the left and right halves to DSI1
  and DSI2 respectively. In order to do this, we need to configure the
  2 Layer Mixers in Source Split mode.

- HDMI 4K: In order to support resolutions with width higher than the
  max width supported by a hwpipe, we club 2 hwpipes together:

hwpipe1 --- LM0 -- DSPP0
       -   -             \
         -                -- 3D Mux -- INTF0 -- HDMI
       -   -             /
hwpipe2 --- LM1 -- DSPP1

  hwpipe1 is staged on the 'left' Layer Mixer, and hwpipe2 is staged on
  the 'right' Layer Mixer. An additional block called the '3D Mux' is
  used to merge the output of the 2 DSPPs to a single interface.
  In this use case, it is possible that a 4K surface is downscaled and
  placed completely within one of the halves. In order to support such
  scenarios (and keep the programming simple), Layer Mixers with Source
  Split can be assigned 2 hw pipes per stage. While scanning out, the HW
  takes care of fetching the pixels fom the correct pipe.

Add a MDP cap to tell whether the HW supports source split or not.
Add a MDP LM cap that tells whether a LM instance can operate in
source split mode (and generate the 'left' part of the display
output).

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