support 24-bit encodings.  simplify the way supported encodings are handled by storing an array of supported encodings.
support 24-bit encodings.  simplify the way supported encodings are
handled by storing an array of supported encodings.

NOTE: this also removes all conversions from this driver.  in
particular, uaudio no longer supports 16-bit big endian encodings,
because the USB audio specification only supports little endian
encodings.

ok ratchov

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars