Audio system preferring surround formats

[nia <nia%NetBSD.org@localhost>]

In audio_hw_probe in sys/dev/audio/audio.c, the default preferred
format will be scored based on the number of hardware channels.

This makes sense for hardware that supports monaural and stereo
formats, so stereo will be preferred.

However, for hardware that supports surround, it can result
in the default format being a surround format, which can
be confusing or not result in proper audio output, e.g.
https://www.unitedbsd.com/d/458-audio-on-macbookpro-2015-for-netbsd

Should this be adjusted to not prefer channels >= 3?