ALSA: virtuoso: add Xonar Essence STX II daughterboard support

Detect and handle the H6 daughterboard; it works the same as with the
ST, except that there is no conflict with the CS2000 chip.

Tested-by: Andreas Allacher <andreas.allacher@gmx.at>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>