refactor(plat/ffa): extract cpu cycles

Change-Id: I3ef0222bbce11ab1b9436d142064ac2d70db01cb
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/src/api.c b/src/api.c
index 695ac5b..d8c91ba 100644
--- a/src/api.c
+++ b/src/api.c
@@ -14,6 +14,7 @@
 #include "hf/arch/mm.h"
 #include "hf/arch/other_world.h"
 #include "hf/arch/plat/ffa.h"
+#include "hf/arch/plat/ffa/cpu_cycles.h"
 #include "hf/arch/plat/ffa/direct_messaging.h"
 #include "hf/arch/plat/ffa/ffa_memory.h"
 #include "hf/arch/plat/ffa/indirect_messaging.h"