V4L/DVB (8996): S2API: typedefs replaced, _SEQ_'s removed, fixed 16 command arrays replaced

After discussion the following changes were made:
1. Removed the typedefs in frontend.h, use structures.
2. In the frontend.h, remove the 16 command limit on the API and
   switch to a flexible variable length API. For practical reasons
   a #define limits this to 64, this should be discussed.
3. Changed dvb-core ioctl handing to deal with variable sequences
   of commands.

tune-v0.0.3.c is required to use this API, it contains the interface changes.

Signed-off-by: Steven Toth <stoth@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>