mdss: mdp: Add programmable fetch for mdp

Currently, MDP fetches only at the vertical backporch.
All through the vertical front porch, hardware sits idle
doing nothing. Starting from MDP v1.5, hardware has the
capability to fetch at the programmable line in the vertical
front porch.

Change-Id: Ib2482fa610acdfc5cbf944415a344c11f313bc81
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>