drm/msm/dp: enable usbpd attention events

Handle the attention events delivered by USBPD from sink.
Read the corresponding status registers from sink to get
the current link status. Fix memory issues while handling
these events to avoid possible crashes.

CRs-Fixed: 2072336
Change-Id: Ic55b8c363c77804831e22a6fe4dd2bbb3c9adb27
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>