media: dvb: mpq: Enhance information exposed in debug-fs

Added the following files to existing demux directory in debug-fs:
1. decoder_out_count: Counts number of frames output to decoder.
2. decoder_out_interval_sum: Sum of time intervals between
   frames outputs.
3. decoder_out_interval_average: Average of time intervals between
   frames outputs.
4. decoder_out_interval_max: Maximum time interval between
   frames outputs.

All counters can read and reset by writing to the respective file.
demux device output in debug-fs was adjusted for better visibility.

Change-Id: I2c9835364c534cc4b9c1cbc74afee71c40f61d98
Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>
Signed-off-by: Neha Pandey <nehap@codeaurora.org>