msm_fb: display: Create sysfs entries in mdp_probe for MDP3 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: I18b05b8d2a65d489afc6e3274ec8dc7a5b9a5f9a
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>