[ALSA] isa_bus: es1688

es1688: port to isa_bus infrastructure. very slight reorganization of
the auto-probe code to be a bit easier on the eye (if not the senses).

Signed-off-by: Rene Herman <rene.herman@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>