hal_audio: Allow writing dump info into pipes

The following HAL methods use file descriptors to write dump
info comprising audioflinger debug dump:

IDevice.debugDump
IEffectsFactory.debugDump
IStream.debugDump

Bug: 36074936
Test: check contents of 'adb shell dumpsys media.audio_flinger'
      on -userdebug builds

Change-Id: Ie2bec95c6b73c6f10941e2b0a95a25d6a7a6e4c1