Juno: Initialize stack protector canary from the trusted entropy source

Change-Id: I7f3e4bfd46613c6311ba4015d56705414fd6feab
Signed-off-by: dp-arm <dimitris.papastamos@arm.com>
diff --git a/plat/arm/board/juno/juno_def.h b/plat/arm/board/juno/juno_def.h
index d7e2ac6..a8e9872 100644
--- a/plat/arm/board/juno/juno_def.h
+++ b/plat/arm/board/juno/juno_def.h
@@ -83,6 +83,7 @@
 #define TRNG_INTMASK	0x14
 #define TRNG_CONFIG	0x18
 #define TRNG_CONTROL	0x1C
+#define TRNG_NBYTES	16	/* Number of bytes generated per round. */
 
 /*******************************************************************************
  * MMU-401 related constants