media/dvb-core: Migrate mpq demux driver from kernel 4.14 to 4.19

This change migrates all the relevant files and updates made
to the dvb/demux framework, required for mpq demux driver.
The snapshot is taken from msm-4.14:
'commit 76ba91 ("Migrate mpq demux driver from kernel 4.9 to 4.14")'
In addition, introduce a few code changes to fix warnings,
typos and other style issues.

Change-Id: I9b78346ed13eb4d8b3d91b9379cfc519fa520693
Signed-off-by: Murthy Nidadavolu <mnssr@codeaurora.org>