It is for channel to slot mapping, and it is not only for 8 channels mapping,
but also in 2, 4 and 6 channels mapping. If we want to use the 2 channels in
the stereo2 adc path, we need to set the item "2/1/3/4" or "2/3/1/4".

It also adds for stereo channel swap. It can map the sterero channels "L/R"
to "R/L", "L/L" or R/R.
Signed-off-by: NOder Chiou <oder_chiou@realtek.com>
Signed-off-by: NMark Brown <broonie@kernel.org>