When "default" PCM and control definitions are overwritten by others
like PulseAudio setup, the original system-default defition is lost.
This is a problem when PA is temporarily (or intentionally) disabled
and user wants to use the default dmix.
This patch adds a new standard definition for the system-default,
"sysdefault". This can be used for fallbacks.
Signed-off-by: Takashi Iwai <tiwai@suse.de>