msm; mdss: increase max sync fence fd count

Current sync fence number is based on the maximum ammount of layers that
MDP can support, however application may send more than one fence
associated to a single layer. Increase the maximum ammount of sync
fences to allow most use cases.

Change-Id: I9b04ea7c864501433af86fe57c742634abfd7872
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>