asoc: sdm660_cdc: register ADSP service notifier for digital codec

register ADSP service notifier for digital codec when it is the only codec
being enabled, so that it can monitor the status of adsp and do specific
operation during SSR/PDR.

Change-Id: I1b4f59d32a11686201f52433ddef0df68da0f008
(cherry picked from commit 1811f63c9c9467ac18a361104e39f45c2612f4bb)
Signed-off-by: Albert I <kras@raphielgang.org>