arm: add a configuration for Odroid-XU

Signed-off-by: Jean-Philippe Brucker <jphilippe.brucker@gmail.com>
arm: exynos 5410 support

Dummy support for the Odroid-XU. The UART is assumed to be initialised.

Signed-off-by: Jean-Philippe Brucker <jphilippe.brucker@gmail.com>
driver: synchronise the CPUs before disabling

An IPI could be lost when a CPU is shutdown before it had time to
inject the IRQ that notifies other cores to disable the hypervisor.

Signed-off-by: Jean-Philippe Brucker <jphilippe.brucker@gmail.com>