[POWERPC] 4xx: EP405 boards support for arch/powerpc

Brings EP405 support to arch/powerpc. The IRQ routing for the CPLD
comes from a device-tree property, PCI is working to the point where
I can see the video card, USB device, and south bridge.

This should work with both EP405 and EP405PC.

I've not totally figured out how IRQs are wired on this hardware
though, thus at this stage, expect only USB interrupts working,
pretty much the same as what arch/ppc did.

Also, the flash, nvram, rtc and temp control still have to be wired.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>