i2c: octeon_i2c: Add I2C controller driver for Octeon

Add support for I2C controllers found on Octeon II/III and Octeon TX
TX2 SoC platforms.

Signed-off-by: Aaron Williams <awilliams@marvell.com>
Signed-off-by: Suneel Garapati <sgarapati@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Aaron Williams <awilliams@marvell.com>
Cc: Chandrakala Chavva <cchavva@marvell.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>

doc/device-tree-bindings/i2c/octeon-i2c.txt

@@ -0,0 +1,24 @@
+* I2C controller embedded in Marvell Octeon platforms
+
+Required properties :
+- compatible : Must be "cavium,octeon-7890-twsi" or a compatible string
+- reg : Offset and length of the register set for the device
+- clocks: Must contain the input clock of the I2C instance
+- #address-cells = <1>;
+- #size-cells = <0>;
+
+Optional properties :
+- clock-frequency : Desired I2C bus clock frequency in Hz. If not specified,
+  the default 100 kHz frequency will be used. As only Normal, Fast and Fast+
+  modes are implemented, possible values are 100000, 400000 and 1000000.
+
+Example :
+
+	i2c0: i2c@1180000001000 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		compatible = "cavium,octeon-7890-twsi";
+		reg = <0x11800 0x00001000 0x0 0x200>;
+		clock-frequency = <100000>;
+		clocks = <&sclk>;
+	};