media: dvb: mpq: Use kthread instead of workqueue

demux used single-threaded workqueue to process TS packets
notified from the HW. Workqueue implementation was changed
so that all work scheduled to workqueues are submitted
to same kworker threads, this result on having TS packet
processing not to be done on demux own thread and compete
with other work scheduled by other drivers. Moved to separate
thread dedicated only for demux.

Change-Id: I37bcfacc54ec998d3fb7daa9768bc1966574aa7a
Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>