ALSA: hda - Fix power-saving during playing beep sound

While playing the digital beep tone, the codec shouldn't be turned
off.  This patch adds proper snd_hda_power_up()/down() calls at each
time when the beep is played or off.

Also, this fixes automatically an unnecessary codec power-up at
detaching the beep device when the beep isn't being played.

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