Add OMAP5432 UEVM board

Add the debug UART support for OMAP5432. Generally, the major difference from omap3/4 is that A15 has the GIC IRQ controller. Since GenericBooter does not touch IRQ, I advise to factor out OMAP UART code to a separate file, and the only difference between the boards will be the UART address (which is 0x48020000 for OMAP5 and 0x49020000 for OMAP3)