ALSA: hda/hdmi: Restrict prompt only for CONFIG_EXPERT

ALSA: hda/hdmi: Restrict prompt only for CONFIG_EXPERT

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

This patch marks the prompt of each HDMI codec driver with
CONFIG_EXPERT, so that they are all enabled when the top-level
CONFIG_SND_HDA_CODEC_HDMI is set.

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

The patch also adds the missing help text to the top-level
CONFIG_SND_HDA_CODEC_HDMI together with the explanation of individual
choices, too.

Fixes: 73cd0490819d ("ALSA: hda/hdmi: Split vendor codec 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/20250806192541.21949-3-tiwai@suse.de