bindings: sound: davinci-mcasp: Add support for optional auxclk-fs-ratio

When McASP is bus master it's reference clock (AUXCLK) might not be a
static clock, but running at a specific FS ratio.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/davinci-mcasp-audio.txt

@@ -44,6 +44,9 @@ Optional properties:
   		 please refer to pinctrl-bindings.txt
 - fck_parent : Should contain a valid clock name which will be used as parent
 	       for the McASP fck
+- auxclk-fs-ratio: When McASP is bus master indicates the ratio between AUCLK
+		   and FS rate if applicable:
+		   AUCLK rate = auxclk-fs-ratio * FS rate
 
 Optional GPIO support:
 If any McASP pin need to be used as GPIO then the McASP node must have: