[ALSA] Add default values for power-saving as Kconfig options

Added CONFIG_SND_AC97_POWER_SAVE_DEFAULT and CONFIG_SND_HDA_POWER_SAVE_DEFAULT
Kconfig options as the default values for power-saving mode of AC97 and
HD-audio drivers, respectively.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>