Introduce spci_vm_count_t for count of VMs.

Change-Id: I4eae492136019c6a39b2d06b59793f021b4e07bb
diff --git a/src/api.c b/src/api.c
index 698e788..ccbeeda 100644
--- a/src/api.c
+++ b/src/api.c
@@ -216,7 +216,7 @@
 /**
  * Returns the number of VMs configured to run.
  */
-int64_t api_vm_get_count(void)
+spci_vm_count_t api_vm_get_count(void)
 {
 	return vm_get_count();
 }