qemu: Initial support for the qemu firmware config interface.

qemu: Initial support for the qemu firmware config interface.

qemu has a special device to pass configuration information
from qemu to the firmware.  This patch adds initial support
the interface, namely some infrastructure, detection code and
a function to query the number of CPUs.

Change-Id: I43ff5f4fbf12334a91422aa38f514a82a1d5219e
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-on: http://review.coreboot.org/3343
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>