V4L/DVB (7651): tuner-xc2028: Several fixes to SCODE

This patch fixes several issues on SCODE:

1) The extracting tool weren't generating the proper tags for SCODE. This
   has almost no effect, since those tags shouldn't be used;

2) DIBCOM52 were using a wrong IF. It should be 5200, instead of 5700;

3) seek_firmware were wanting an exact match for firmware type. This is
   wrong. As result, no SCODE firmware were loaded;

4) A few files were including the wrong file for seeking demod firmwares;

5) XC3028_FE_DEFAULT can be used, if user doesn't want to load a firmware.
   However, this weren't documentated. This feature require more testing.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>