Move comments to better locations, de-duplicate, fix/remove incorrect/
outdated ones, add new ones, and unify spacing somewhat.

While at it, also add testing credits for Jonathan Dowland (SB Live!
Platinum) and myself (E-MU 0404b).
Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230422161021.1143903-2-oswald.buddenhagen@gmx.deSigned-off-by: Takashi Iwai <tiwai@suse.de>