V4L/DVB (5208): Kthread API conversion for dvb_frontend and av7110

dvb kernel_thread to kthread API port.  
It is running fine here, including module load/unload and software suspend
(which doesn't work as expected with or without this patch :).
I didn't convert the dvb_ca_en50221 as I do not have such an interface, but
if the conversion process is fine with the v4l-dvb maintainers, it should not
be a problem to send a patch for that too ...
Acked-by: Oliver Endriss <o.endriss@gmx.de>

Signed-off-by: Herbert Poetzl <herbert@13thfloor.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>