i2c: mvtwsi: Add compatibility to DM

This patch adds the necessary functions and Kconfig entry to make the
MVTWSI I2C driver compatible with the driver model.

A possible device tree entry might look like this:

i2c@11100 {
	compatible = "marvell,mv64xxx-i2c";
	reg = <0x11000 0x20>;
	clock-frequency = <100000>;
	u-boot,i2c-slave-addr = <0x0>;
};

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
index 6e22bba..b3e8405 100644
--- a/drivers/i2c/Kconfig
+++ b/drivers/i2c/Kconfig
@@ -154,6 +154,13 @@
 	  Support for UniPhier FIFO-builtin I2C controller driver.
 	  This I2C controller is used on PH1-Pro4 or newer UniPhier SoCs.
 
+config SYS_I2C_MVTWSI
+	bool "Marvell I2C driver"
+	depends on DM_I2C
+	help
+	  Support for Marvell I2C controllers as used on the orion5x and
+	  kirkwood SoC families.
+
 source "drivers/i2c/muxes/Kconfig"
 
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