KVM: arm/arm64: vgic: expose (un)lock_all_vcpus

We need to use those helpers in vgic-its.c so let's
expose them in the private vgic header.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Christoffer Dall <cdall@linaro.org>