[media] em28xx: improve USB endpoint logic, also use bulk transfers

The current enpoint logic ignores all bulk endpoints and uses
a fixed mapping between endpint addresses and the supported
data stream types (analog/audio/DVB):
  Ep 0x82, isoc	=> analog
  Ep 0x83, isoc	=> audio
  Ep 0x84, isoc	=> DVB
Now that the code can also do bulk transfers, the endpoint
logic has to be extended to also consider bulk endpoints.
The new logic preserves backwards compatibility and reflects
the endpoint configurations we have seen so far:
  Ep 0x82, isoc		=> analog
  Ep 0x82, bulk		=> analog
  Ep 0x83, isoc*	=> audio
  Ep 0x84, isoc		=> digital
  Ep 0x84, bulk		=> analog or digital**
 (*: audio should always be isoc)
 (**: analog, if ep 0x82 is isoc, otherwise digital)

[mchehab@redhat.com: Fix a CodingStyle issue: don't break strings
 into separate lines]

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>