MLKU-24-9 sound: soc: fix unused warning

When CONFIG_PM is not defined, the runtime suspend and resume
are unused so we should use __maybe_unused attribute.

Signed-off-by: Cosmin-Gabriel Samoila <cosmin.samoila@nxp.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
(cherry picked from commit 2d68f7cc)