drm/msm/mdp5: Remove mixer/intf pointers from mdp5_ctl

These are a part of CRTC state, it doesn't feel nice to leave them
hanging in mdp5_ctl struct. Pass mdp5_pipeline pointer instead
wherever it is needed.

We still have some params in mdp5_ctl like start_mask etc which
are derivative of atomic state, and should be rolled back if
a commit fails, but it doesn't seem to cause much trouble.

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