[ALSA] emu10k1 driver - add multichannel device hw:x,3 [1/8]

EMU10K1/EMU10K2 driver
Update header file for multichannel support.
Add some new register info.
Signed-Off-By: Lee Revell <rlrevell@joe-job.com>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>