drm/msm/dp: clean up hdcp threads

Currently, sde-hdcp2p2 and dp-hdcp2p2 modules maintain their
own threads and queue different works based on the functionalities
they are going to perform. These threads support executing only
one work at a given time. To simplify the implementation, remove
all the works that these threads execute. Instead implement just
one main work that is run continuously on each of these thread.
The threads go to sleep if not being executed. To support the
asynchronous behavior of these threads, implement a fifo queue.
This queue manages the commands to be executed by the thread.
Every time a command is queued to the queue, the thread is pinged
to execute it.

CRs-Fixed: 2393144d
Change-Id: Iee3522f06934c753cda19d13d9bee65b41d6b407
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>