V4L/DVB (8988): S2API: Allow the properties to call legacy ioctls

SET_TONE and SET_VOLTAGE were not previously implemented. Two options
existed. Either cut/paste from the previous ioctl handler into the
process_properties function, which is code duplication. Or, split
the current ioctl handler into it's two major pieces.

Piece 1, responsible for input validation and semaphore acquiring
Piece 2 the processing of the previous ioctls

and finally, a new third pieces where the array of properties
is processed, and can freely call the legacy ioctl handler without
having to re-acquire the fepriv->sem semaphore. This is a clean approach
and ensures the existing legacy ioctls are processed as they were previously
(but with an extra function call) and allows the new API to share code
without duplication.

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