V4L/DVB (7730): tuner-xc2028: Fix SCODE load for MTS firmwares

There are different tables for MTS firmwares. This should be taken into
account while selecting the proper firmware.

While at tuner-xc2028.h, improve some comments.

Thanks to Edward J. Sheldrake <ejs1920@yahoo.co.uk> for helping to
diagnose such troubles with PAL/I standard.

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