mdss: Add MDP_SMP_FORCE_ALLOC mdp flag

MDP_SMP_FORCE_ALLOC flag is used to allow SMP
allocations even when there is mismatch between
allocated and requested SMPs for a pipe.
User space can make use of this flag in extreme scenarios
where SMP allocations need to pass like GPU composition
and playback of protected  or secure videos.

Change-Id: I369b4361e7e2bbfc8150add467678c4ef8d5cfb6
Signed-off-by: Justin Philip <jphili@codeaurora.org>