For allowing the build without CONFIG_PM, add definitions of dummy
functions for snd_ac97_suspend() and snd_ac97_resume() without
CONFIG_PM, too.

Link: https://lore.kernel.org/r/20230330132847.12882-1-tiwai@suse.deReviewed-by: Jaroslav Kysela <perex@perex.cz>
Reviewed-by: Tasos Sahanidis <tasos@tasossah.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>