[media] drxk: Improves the UIO handling

The driver is too limited: it assumes that UIO is used only for
controlling the antenna, and that only UIO-1 is in usage. However,
from Terratec H7 driver [1], 3 UIO's can be used. In fact, it seems
that H7 needs to use all 3. So, make the code generic enough to handle
the most complex scenario. For now, only antena GPIO can be specified,
but is is easier now to add the other GPIO/UIO needs.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>