ASoC: mchp, i2s-mcc: Add property to specify pin pair for TDM

SAMA7G5's I2S-MCC has 4 pairs of DIN/DOUT pins. Since TDM only uses a
single pair of pins for synchronous capture and playback, the controller
needs to be told which of the pair is connected. This can be mentioned
using the new "microchip,tdm-data-pair" property. The property is optional,
needed only if TDM is used, and if it's missing DIN/DOUT 0 pins will be
used by default.
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Link: https://lore.kernel.org/r/20210301170905.835091-5-codrin.ciubotariu@microchip.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/mchp-i2s-mcc.txt

@@ -19,7 +19,12 @@ Required properties:
 Optional properties:
 - pinctrl-0:      Should specify pin control groups used for this controller.
 - princtrl-names: Should contain only one value - "default".
-
+- microchip,tdm-data-pair: 8 bit value that represents the DIN/DOUT pair pins
+			   which are used to receive/send TDM data. It is optional
+			   and it is only needed if the controller uses the TDM
+			   mode. Not available for "microchip,sam9x60-i2smcc"
+			   compatible. If it's not present, the default value is 0,
+			   so the DIN/DOUT 0 pins are used.
 
 (1) : Only the peripheral clock is required. The generated clock is optional
       and should be set mostly when Master Mode is required.