msm_fb: display: Create sysfs entries in mdp_probe for MDP4 targets

vsync sysfs entries should be created in mdp_probe instead of
creating in panel on. This avoids waiting for the first event
control in framework

Change-Id: I3b6987555a2318f1bd36be253349611e051ca58d
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>