V4L/DVB (12291): b2c2: fix frontends compiled into kernel

A recent patch didn't take into account that frontends can be compiled into
the kernel.  Or that frontends compiled as modules can't be used by the
b2c2 driver if it is not a module itself.

Some frontends require multiple drivers, e.g. a demod driver and a tuner
driver.  The code for the frontend support was getting added if the demod
driver was available.  Change this to also require any needed tuner or SEC
drivers as well.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>