drm/msm/dp: check if framework is ready before notifying DP connect

As part of the DP attention callback from USB driver to DisplayPort
driver, check if framework is ready before notifying userspace for
DisplayPort connect event. This is needed to make sure that
DisplayPort comes up fine on device bootup with cable connected.

Change-Id: Iede094855000e2b878a90507d819205e0dd02ccd
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>