Refactor mdp5_plane_mode_set to call mdp5_hwpipe_mode_set. The latter
func takes in only the hwpipe and the parameters that need to be
programmed into the hwpipe registers. All the code that calculates these
parameters is left as is in mdp5_plane_mode_set.

In the future, when we let drm_plane be comprised of 2 hwpipes, this func
allow us to configure each pipe without adding redundant code.
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>