ALSA: hda: realtek: Reduce CONFIG_PM dependencies

CONFIG_PM dependencies got reduced in HD-audio codec core driver, and
now it's time to reduce in HD-audio realtek codec driver, too.

Simply drop CONFIG_PM ifdefs.  A superfluous __maybe_unused attribute
was dropped as well.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20240506161359.6960-11-tiwai@suse.de