ALSA: ice1712: add chip_exit callback

Add chip_exit callback to allow card subdrivers to do cleanup work on module
removal.

Needed by Philips PSC724 subdriver to cancel delayed work.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>