foundation: disable Scalable Vector Extension (SVE)

When foundation platform is booted with SVE enabled in linux
kernel and with Xen hypervisor, linux kernel is stopped by a
trap catched by Xen during early boot as Xen is configuring
the coprocessor to trap access to SVE to EL2.Disabling the SVE
in foundation to boot the guest and host.

Change-Id: I862540a46686f1fb5343a3143da61db6073bb1d3
Signed-off-by: Rahul Singh <rahul.singh@arm.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>