ALSA: emu10k1: omit non-applicable mixer controls for E-MU cards

The E-MU cards don't try very hard to be Sound Blasters. All sound I/O
goes through the Hana FPGA, thus making the regular extin/out controls
useless. Still showing them just serves to clutter up the interface and
confuse the user.
Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230514170323.3408834-5-oswald.buddenhagen@gmx.deSigned-off-by: Takashi Iwai <tiwai@suse.de>