For documentation purposes and later use.

Some pre-existing but (mostly) unused definitions were renamed for
consistency.
Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230422161021.1143903-6-oswald.buddenhagen@gmx.deSigned-off-by: Takashi Iwai <tiwai@suse.de>