drm/msm/dp: process link update with cp irq

In some cases, sink can issue CP (Content Protection) interrupt
along with link update interrupt. Handle link update request first
and then cp irq to make sure link has been updated properly before
re-authentication.

Change-Id: I9fc14b426f20eb3c08dc64f2787a7acd2f5cfa06
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>