V4L/DVB: Add FE_CAN_TURBO_FEC

Some (North American) providers use a non-standard mode called
"8psk turbo fec". Since there is no flag in the driver that
would allow an application to determine whether a particular
device can handle "turbo fec", the attached patch introduces
FE_CAN_TURBO_FEC.

Since there is no flag in the SI data that would indicate
that a transponder uses "turbo fec", VDR will assume that
all 8psk transponders on DVB-S use "turbo fec".

Tested-by: Derek Kelly <user.vdr@gmail.com>
Signed-off-by: Klaus Schmidinger <Klaus.Schmidinger@tvdr.de>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>