msm_fb: Handle vsync interrupt properly on MDP 3.03 targets

Handle enabling/disabling the vsync interrupt and mdp clock
enabling/disabling in a better way on MDP 3.03 targets. This
will avoid target crashes due to unclocked register access.

CRs-fixed: 388751
Change-Id: I5c4a409772464ce7d06869374dcba5ad7e335955
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>