cactus: ivy: Add sleep service

This service sleeps for a number of milliseconds.

Change-Id: Ib7f17142d22c8313dedc5f8037874bacbf8ed5f4
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/spm/cactus/cactus_def.h b/spm/cactus/cactus_def.h
index ef813d2..13b5dac 100644
--- a/spm/cactus/cactus_def.h
+++ b/spm/cactus/cactus_def.h
@@ -52,6 +52,8 @@
 #define CACTUS_PRINT_MAGIC		U(1)
 /* Return a magic number unique to Cactus */
 #define CACTUS_GET_MAGIC		U(2)
+/* Sleep for a number of milliseconds */
+#define CACTUS_SLEEP_MS			U(3)
 
 #define CACTUS_MAGIC_NUMBER		U(0x12481369)