ALSA: hda: Move HD-audio core stuff into sound/hda/core

This is a part of HD-audio code restructuring.
Simply move the current code of sound/hda/* into the subdirectory
sound/hda/core, so that more stuff can be moved into sound/hda cleanly
later.

Most of file names with hdac_ and hdac_ext_ prefix are renamed without
the prefix, since they can be identified well in the directory name
and superfluous.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250709160434.1859-3-tiwai@suse.de