Tidying FFA helpers

Moved SP specific functions/macros to "sp_helpers.c/h".
Placed ffa interfaces/symbols shared between tftf and SPs in
"ffa_helpers.c/h".

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I4cf967f87837ce3e7d0f7244f9cc0677f608f9cd
diff --git a/spm/cactus/cactus_debug.c b/spm/cactus/cactus_debug.c
index 91fbfda..43093a6 100644
--- a/spm/cactus/cactus_debug.c
+++ b/spm/cactus/cactus_debug.c
@@ -6,9 +6,9 @@
 
 #include <drivers/arm/pl011.h>
 #include <drivers/console.h>
+#include <sp_helpers.h>
 
 #include "cactus.h"
-#include "ffa_helpers.h"
 
 static int (*putc_impl)(int);