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/include/plat/arm/css/common/css_def.h b/include/plat/arm/css/common/css_def.h
index e3dd2b0..157a22f 100644
--- a/include/plat/arm/css/common/css_def.h
+++ b/include/plat/arm/css/common/css_def.h
@@ -58,10 +58,9 @@
 /* Interrupt handling constants */
 #define CSS_IRQ_MHU			69
 #define CSS_IRQ_GPU_SMMU_0		71
-#define CSS_IRQ_GPU_SMMU_1		73
-#define CSS_IRQ_ETR_SMMU		75
 #define CSS_IRQ_TZC			80
 #define CSS_IRQ_TZ_WDOG			86
+#define CSS_IRQ_SEC_SYS_TIMER		91
 
 /*
  * SCP <=> AP boot configuration