alsa-mixer: sb-omni-surround-5.1.conf: remove analog-surround-21, add Linux 4.3+...

alsa-mixer: sb-omni-surround-5.1.conf: remove analog-surround-21, add Linux 4.3+ support

In 2.1 mode LFE is not actually working at all, so it is removed.
With Linux 4.3-rc1+ Mic/Line are hw:%f,0,0 as it should be: https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/commit/sound/usb?id=5ee20bc792467d7d612157e0a9962765aa943b08
So now we support both Linux 4.2.x- and 4.3-rc1+ setups.
Also in Linux 4.3-rc1 S/PDIF input was detected incorrectly (there is no such hardware input), so it is not present in config.