drm/msm/mdp5: Remove the pipeline stuff in mdp5_ctl

The mdp5_ctl has an 'op_mode' struct which contains info on
the downstream pipeline.

Grouping these params together in a struct doesn't serve much
purpose in the code. Maybe there was a plan to expand this
further that never happened.

Remove the op_mode struct, and place its members directly in
mdp5_ctl. This will help avoid confusion later when I introduce
my own verion of a mdp5 pipeline :)

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