pcm: Fix DSD formats userland usability

Support for DSD sample formats has been added a while ago. This patch makes
those sample formats beter usable from userland (e.g. aplay).

[These implementation details have been forgotten in the previous DSD
 support patch -- tiwai]

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Sync include/sound/asound.h with 3.17-rc1 kernel

Signed-off-by: Takashi Iwai <tiwai@suse.de>
pcm: Add missing signed and endianess definitions for DSD formats

Signed-off-by: Takashi Iwai <tiwai@suse.de>