I2C for OMAP platforms

Required properties :
- compatible : Must be "ti,omap2420-i2c", "ti,omap2430-i2c", "ti,omap3-i2c"
  or "ti,omap4-i2c"
- ti,hwmods : Must be "i2c<n>", n being the instance number (1-based)
- #address-cells = <1>;
- #size-cells = <0>;

Recommended properties :
- clock-frequency : Desired I2C bus clock frequency in Hz. Otherwise
  the default 100 kHz frequency will be used.

Optional properties:
- Child nodes conforming to i2c bus binding

Note: Current implementation will fetch base address, irq and dma
from omap hwmod data base during device registration.
Future plan is to migrate hwmod data base contents into device tree
blob so that, all the required data will be used from device tree dts
file.

Examples :

i2c1: i2c@0 {
    compatible = "ti,omap3-i2c";
    #address-cells = <1>;
    #size-cells = <0>;
    ti,hwmods = "i2c1";
    clock-frequency = <400000>;
};
