[media] Add support for TechniSat Skystar S2

This patch adds support for the Technisat Skystar S2 - this
has been tried before but the cx24120 driver was a bit out of shape
and it didn't got any further:

https://patchwork.linuxtv.org/patch/10575/



It is an old card, but currently being sold off for next to nothing,
so it's proving quite popular of late. Noticing it's quite similar
to the cx24116 and cx24117 I've rewritten the driver in a similar way.

There were a few registers and commands from those drivers
missing from this one I've tested out and found they do something so
they've been added in to speed up tuning and to make get_frontend
return something useful.

Signed-off-by: Jemma Denson <jdenson@gmail.com>
Signed-off-by: Patrick.Boettcher <patrick.boettcher@posteo.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>