firmware: audio_mixer: Fix issue with planar audio when output channels needed expansion

hdmi: Include requested mode and allow hdmi drive when edid fails
See: http://openelec.tv/forum/124-raspberry-pi/71491-4-0-4-passthru-audio-50-working-chance

tvservice: More accurate description of standby message
See: https://github.com/raspberrypi/firmware/issues/286