xen/arm: implement HYPERVISOR_vcpu_op

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Ian Campbell <ian.campbell@citrix.com>

arch/arm/xen/hypercall.S

@@ -87,6 +87,7 @@ HYPERCALL2(event_channel_op);
 HYPERCALL2(hvm_op);
 HYPERCALL2(memory_op);
 HYPERCALL2(physdev_op);
+HYPERCALL3(vcpu_op);
 
 ENTRY(privcmd_call)
 	stmdb sp!, {r4}