dt-bindings: i2c: at91: add binding for enable-dig-filt

Add binding specificatoin for digital filter inside the i2c controller

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>

Author: ehristev

Documentation/devicetree/bindings/i2c/i2c-at91.txt

@@ -20,6 +20,9 @@ Optional properties:
   capable I2C controllers.
 - i2c-sda-hold-time-ns: TWD hold time, only available for "atmel,sama5d4-i2c"
   and "atmel,sama5d2-i2c".
+- enable-dig-filt: Enable the built-in digital filter on the i2c lines,
+  specifically required depending on the hardware PCB/board and if the
+  version of the controller includes it.
 - Child nodes conforming to i2c bus binding
 
 Examples :
@@ -56,6 +59,7 @@ i2c0: i2c@f8034600 {
 	clocks = <&flx0>;
 	atmel,fifo-size = <16>;
 	i2c-sda-hold-time-ns = <336>;
+	enable-dig-filt;
 
 	wm8731: wm8731@1a {
 		compatible = "wm8731";