powerpc/book3e: Add Chroma as a new WSP/PowerEN platform.

This patch add the Chroma platform to WSP/PowerEN, which is a PCIe
card (a defconfig is included).

The card includes an H8 service processor that is used to manage the
card.  The H8 is connected over the second serial UART on the PowerEN
chip so this patch includes a simple 16550 driver to enable
communication, mostly for "power off" and "rebooting".

This patch also includes a, WSP specific, "halt" method that will shut
of all A2 cores but still leave power on at the chip level.  This is
desirable, especially if you wish to interrogate the chip with a
hardware probe after the halt.

Signed-off-by: Jimi Xenidis <jimix@pobox.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>