[ALSA] Support 3-bytes 24bit format in PCM OSS emulation

Add the support of 3-bytes 24bit formats in PCM OSS emulation.
Also removed snd_pcm_build_linear_format() function.  It's exported
just for OSS emulation, and now the code was changed without calling
this function.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>