Introduce typedef for [v]CPU IDs.

Change-Id: I99988988d8ac57c688c5fd52f072357202255f18
diff --git a/inc/hf/boot_params.h b/inc/hf/boot_params.h
index 591e353..ee46777 100644
--- a/inc/hf/boot_params.h
+++ b/inc/hf/boot_params.h
@@ -31,7 +31,7 @@
 };
 
 struct boot_params {
-	uint64_t cpu_ids[MAX_CPUS];
+	cpu_id_t cpu_ids[MAX_CPUS];
 	size_t cpu_count;
 	struct mem_range mem_ranges[MAX_MEM_RANGES];
 	size_t mem_ranges_count;