As each DVBv3 call may generate an stats overhead, prevent doing
it too fast. This is specially useful if a burst of get stats
DVBv3 call is sent.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

To avoid mixing two different things at the same place, move the
debugfs code into a separate file.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>