ALSA: emu10k1: clarify various fx8010.*_mask fields

ALSA: emu10k1: clarify various fx8010.*_mask fields

extin_mask and extout_mask are used only by the SbLive! microcode, so
they have no effect on Audigy.

Eliminate fxbus_mask entirely, as it wasn't actually used for anything.

As a drive-by, remove the pointless pad1 field from struct
snd_emu10k1_fx8010 - it is not visible to user space, so it has no
binary compatibility constraints.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230421141006.1005509-1-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>