dt-bindings: i2c: I2C binding for Mellanox BlueField SoC

Add device tree bindings documentation for Mellanox BlueField
I2C SMBus controller.
Signed-off-by: Khalil Blaiech <kblaiech@mellanox.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Documentation/devicetree/bindings/i2c/mellanox,i2c-mlxbf.txt

+Device tree configuration for the Mellanox I2C SMBus on BlueField SoCs
+
+Required Properties:
+
+- compatible : should be "mellanox,i2c-mlxbf1" or "mellanox,i2c-mlxbf2".
+
+- reg : address offset and length of the device registers. The
+	registers consist of the following set of resources:
+		1) Smbus block registers.
+		2) Cause master registers.
+		3) Cause slave registers.
+		4) Cause coalesce registers (if compatible isn't set
+		   to "mellanox,i2c-mlxbf1").
+
+- interrupts : interrupt number.
+
+Optional Properties:
+
+- clock-frequency : bus frequency used to configure timing registers;
+			allowed values are 100000, 400000 and 1000000;
+			those are expressed in Hz. Default is 100000.
+
+Example:
+
+i2c@2804000 {
+	compatible = "mellanox,i2c-mlxbf1";
+	reg =	<0x02804000 0x800>,
+		<0x02801200 0x020>,
+		<0x02801260 0x020>;
+	interrupts = <57>;
+	clock-frequency = <100000>;
+};
+
+i2c@2808800 {
+	compatible = "mellanox,i2c-mlxbf2";
+	reg =	<0x02808800 0x600>,
+	        <0x02808e00 0x020>,
+		<0x02808e20 0x020>,
+		<0x02808e40 0x010>;
+	interrupts = <57>;
+	clock-frequency = <400000>;
+};