Remove IRQ_SEC_SGI_8 constant

In both FVP and Juno ports, IRQ #16, which is a PPI, is incorrectly
identified as secure SGI #8 through the constant IRQ_SEC_SGI_8.
This patch removes it.

Fixes ARM-software/tf-issues#282

Change-Id: I9e52d849611ffcd2b1f28e56dd156c5b217ed63e
diff --git a/plat/fvp/fvp_def.h b/plat/fvp/fvp_def.h
index 99c23d8..06f2a64 100644
--- a/plat/fvp/fvp_def.h
+++ b/plat/fvp/fvp_def.h
@@ -209,7 +209,6 @@
 #define IRQ_SEC_SGI_5			13
 #define IRQ_SEC_SGI_6			14
 #define IRQ_SEC_SGI_7			15
-#define IRQ_SEC_SGI_8			16
 
 /*******************************************************************************
  * PL011 related constants
diff --git a/plat/juno/juno_def.h b/plat/juno/juno_def.h
index 88e35b0..e205498 100644
--- a/plat/juno/juno_def.h
+++ b/plat/juno/juno_def.h
@@ -143,7 +143,6 @@
 #define IRQ_SEC_SGI_5			13
 #define IRQ_SEC_SGI_6			14
 #define IRQ_SEC_SGI_7			15
-#define IRQ_SEC_SGI_8			16
 
 /*******************************************************************************
  * PL011 related constants