drm/msm: add notification for bridge enable/disable

Add notification block chain support for suspend/resume
events in DRM driver, which can be used by other kernel
modules such as touch driver to get notified about display
suspend/resume state transitions.

Change-Id: Iec9c46363707b3fa8e09203eca95427c95f81c7c
Signed-off-by: Yuan Zhao <yzhao@codeaurora.org>