Introduce typedef for vCPU index.

Change-Id: I51194706edb86811487f2a22b3bda5405e605b5e
diff --git a/inc/hf/vm.h b/inc/hf/vm.h
index 4bebc20..bd8a905 100644
--- a/inc/hf/vm.h
+++ b/inc/hf/vm.h
@@ -102,4 +102,4 @@
 struct vm *vm_find(spci_vm_id_t id);
 struct vm_locked vm_lock(struct vm *vm);
 void vm_unlock(struct vm_locked *locked);
-struct vcpu *vm_get_vcpu(struct vm *vm, uint32_t vcpu_index);
+struct vcpu *vm_get_vcpu(struct vm *vm, spci_vcpu_index_t vcpu_index);