lavu/log: add device categories

Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>
lavd: add categories to device implementations

Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>
lavd/avdevice: add device iterators

Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>
Merge remote-tracking branch 'lukaszmluki/master'

* lukaszmluki/master:
  lavd/avdevice: add device iterators
  lavd: add categories to device implementations
  lavu/log: add device categories

Merged-by: Michael Niedermayer <michaelni@gmx.at>