pcm: add and describe SND_PCM_FORMAT_{S, U}20

pcm: add and describe SND_PCM_FORMAT_{S, U}20

This patch adds and describes in various functions that query format
properties SND_PCM_FORMAT_{S,U}20 formats that were recently added to the
kernel as SNDRV_PCM_FORMAT_{S,U}20.

These formats are similar to existing 20-bit PCM formats
SND_PCM_FORMAT_{S,U}20_3, however they occupy 4 bytes instead of 3.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>