V4L/DVB (10164): Add missing S2 caps flag to S2API

The attached patch adds a capability flag that allows an application
to determine whether a particular device can handle "second generation
modulation" transponders. This is necessary in order for applications
to be able to decide which device to use for a given channel in
a multi device environment, where DVB-S and DVB-S2 devices are mixed.

It is assumed that a device capable of handling "second generation
modulation" can implicitly handle "first generation modulation".
The flag is not named anything with DVBS2 in order to allow its
use with future DVBT2 devices as well (should they ever come).

Signed-off by: Klaus Schmidinger <Klaus.Schmidinger@cadsoft.de>

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