ARM: enable ARMv7 virt support for the Arndale board

To enable hypervisors utilizing the ARMv7 virtualization extension
on the Arndale board, add the simple SMP pen address writer function
and add the required configuration variables to switch all cores to
HYP mode before launching the OS.
This allows booting KVM and Xen directly from u-boot.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>