[media] remove include/linux/dvb/dmx.h

The only reason for this header is to make sure that include
linux/time.h were added before uapi/*/dmx.h. Just push down the
time.h header on the few places where this is used, and drop
this new header.

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