Introduce spci_vm_count_t for count of VMs.

Change-Id: I4eae492136019c6a39b2d06b59793f021b4e07bb
diff --git a/inc/vmapi/hf/call.h b/inc/vmapi/hf/call.h
index 239244f..01be71f 100644
--- a/inc/vmapi/hf/call.h
+++ b/inc/vmapi/hf/call.h
@@ -56,7 +56,7 @@
 /**
  * Returns the number of secondary VMs.
  */
-static inline int64_t hf_vm_get_count(void)
+static inline spci_vm_count_t hf_vm_get_count(void)
 {
 	return hf_call(HF_VM_GET_COUNT, 0, 0, 0);
 }