Introduce typedef for [v]CPU IDs.

Change-Id: I99988988d8ac57c688c5fd52f072357202255f18
diff --git a/src/fdt_handler.c b/src/fdt_handler.c
index a87226e..db8c0ef 100644
--- a/src/fdt_handler.c
+++ b/src/fdt_handler.c
@@ -126,7 +126,7 @@
 	return true;
 }
 
-void fdt_find_cpus(const struct fdt_node *root, uint64_t *cpu_ids,
+void fdt_find_cpus(const struct fdt_node *root, cpu_id_t *cpu_ids,
 		   size_t *cpu_count)
 {
 	struct fdt_node n = *root;