ALSA: hda - Adjust power of beep widget and outputs

As the widget PM may turn off the pins, this might lead to the silent
output for beep when no explicit paths are given.  This patch adds
fake output paths for the beep widget so that the output pins are
dynamically powered upon beep on/off.

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