media: dvb uAPI docs: minor editorial changes

media: dvb uAPI docs: minor editorial changes

Do minor editorial changes to improve documentation readability:

- mark literals as such;
- add table markups to hint sizes;
- define what PES means;
- instead of hardcoding devnode numbers to zero (like adapter0/) use a
  question mark, to indicate that multiple devnodes may exist;
- add cross-references where useful.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>