media: dvb_frontend: add physical layer scrambling support

This commit adds a new property DTV_SCRAMBLING_SEQUENCE_INDEX.

This 18 bit field, when present, carries the index of the DVB-S2 physical
layer scrambling sequence as defined in clause 5.5.4 of EN 302 307.
There is no explicit signalling method to convey scrambling sequence index
to the receiver. If S2 satellite delivery system descriptor is available
it can be used to read the scrambling sequence index (EN 300 468 table 41).

By default, gold scrambling sequence index 0 is used. The valid scrambling
sequence index range is from 0 to 262142.

Increase the DVB API version in order userspace to be aware of the changes.

Signed-off-by: Athanasios Oikonomou <athoik@gmail.com>
Acked-by: Ralph Metzler <rjkm@metzlerbros.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>