ALSA: hda/cirrus: Restrict prompt only for CONFIG_EXPERT

The split of Cirrus HD-audio codec driver may confuse users when
migrating from the previous kernel configs and leave the needed
drivers disabled.  Although we've already set y as default, it's still
safer to paper over the wrong choices.

This patch marks the prompt of split CS420x and CS421x codec drivers
with CONFIG_EXPERT, so that they are all enabled when the top-level
CONFIG_SND_HDA_CODEC_CIRRUS is set.

For users who really care about the minimalistic configuration, they
can turn each driver on/off individually after setting
CONFIG_EXPERT=y.

This patch adds the missing help text to the top-level
CONFIG_SND_HDA_CIRRUS_CODEC together with the explanation of
individual choices, and corrects the help texts that don't fit well
nowadays, too.

Fixes: 1cb8744a ("ALSA: hda/cirrus: Split to cs420x and cs421x drivers")
Link: https://lore.kernel.org/10172c80-daec-4e20-ab57-a483cf1afc02@molgen.mpg.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250806192541.21949-4-tiwai@suse.de