ALSA: emu10k1: add toggles for E-mu 1010 optical ports

The optical ports on the E-mu 1010 (and dock) can be configured
for ADAT- or S/PDIF-mode, which is currently hardcoded to ADAT.
Add two mixer elements to expose this setting.
Tested on an E-mu 1010 PCIe with connected Micro Dock.

Signed-off-by: Michael Gernoth <michael@gernoth.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>