OMAP UART controller

Required properties:
- compatible : should be "ti,omap2-uart" for OMAP2 controllers
- compatible : should be "ti,omap3-uart" for OMAP3 controllers
- compatible : should be "ti,omap4-uart" for OMAP4 controllers
- ti,hwmods : Must be "uart<n>", n being the instance number (1-based)

Optional properties:
- clock-frequency : frequency of the clock input to the UART
