drm/msm/dp: synchronize the usbpd and drm events

USBPD delivers cable connect/disconnect and other sink related
events. Based on these events, DRM framework issues enable/disable
events. Both USBPD and DRM execute in different threads and depends
on each other. Synchronize USBPD and DRM events to handle different
use cases involving cable connect/disconnect.

CRs-Fixed: 2072336
Change-Id: I88a2e1b72f3ef39438ade5b30997b18b53f07ce2
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>