kvmtool

This patch enables the Scalable Vector Extension for the guest when
the host supports it.

This requires use of the new KVM_ARM_VCPU_FINALIZE ioctl before the
vcpu is runnable, so a new hook kvm_cpu__configure_features() is
added to provide an appropriate place to do this work.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>