Configure all secure interrupts on ARM platforms

ARM TF configures all interrupts as non-secure except those which
are present in irq_sec_array. This patch updates the irq_sec_array
with the missing secure interrupts for ARM platforms.

It also updates the documentation to be inline with the latest
implementation.

Fixes ARM-software/tf-issues#312

Change-Id: I39956c56a319086e3929d1fa89030b4ec4b01fcc
diff --git a/plat/arm/board/fvp/fvp_def.h b/plat/arm/board/fvp/fvp_def.h
index 6929481..9a9eebf 100644
--- a/plat/arm/board/fvp/fvp_def.h
+++ b/plat/arm/board/fvp/fvp_def.h
@@ -115,7 +115,8 @@
 #define BASE_GICH_BASE			0x2c010000
 #define BASE_GICV_BASE			0x2c02f000
 
-#define IRQ_TZ_WDOG			56
+#define FVP_IRQ_TZ_WDOG			56
+#define FVP_IRQ_SEC_SYS_TIMER		57
 
 
 /*******************************************************************************