Platform: cmsis: Modify stack section name for gcc and iar.

Since stack section naming is ARM_LIB_STACK, Use this naming for
gcc and iar (same as armclang). With this fix, the startup in .c
for fvp_see300 working for armclang can be used for gcc and iar.

Change-Id: I737122981d4562e9eaa82a299b3f6c4cbf06411b
Signed-off-by: Michel Jaouen <michel.jaouen@st.com>
diff --git a/platform/ext/cmsis/cmsis_gcc.h b/platform/ext/cmsis/cmsis_gcc.h
index 2a0999d..7443480 100644
--- a/platform/ext/cmsis/cmsis_gcc.h
+++ b/platform/ext/cmsis/cmsis_gcc.h
@@ -167,11 +167,11 @@
 #endif
 
 #ifndef __INITIAL_SP
-#define __INITIAL_SP              __StackTop
+#define __INITIAL_SP              Image$$ARM_LIB_STACK$$ZI$$Limit
 #endif
 
 #ifndef __STACK_LIMIT
-#define __STACK_LIMIT             __StackLimit
+#define __STACK_LIMIT             Image$$ARM_LIB_STACK$$ZI$$Base
 #endif
 
 #ifndef __VECTOR_TABLE