msm: mdss: switch mdp context between active-only and active+sleep

This change modifies MDP vote to go to Active-Only in
an early stage when bandwidth is not needed and updates
the vote to Active+Sleep when bandwidth must be guaranteed.

Change-Id: I6ccb7a225f97416128518c990d881fa139ec1963
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>