disp: msm: dp: register for USB notifications

Register for USB cable notifications so we can manually trigger
a disconnect event if the USB cable is disconnected during a
simulation.

Change-Id: I08a9313bcde3e74f2a76804e934423e0fc2d6ab6
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>