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_iccarm.h b/platform/ext/cmsis/cmsis_iccarm.h
index 0627a15..4cdd33d 100644
--- a/platform/ext/cmsis/cmsis_iccarm.h
+++ b/platform/ext/cmsis/cmsis_iccarm.h
@@ -248,11 +248,11 @@
 #endif
 
 #ifndef __INITIAL_SP
-#define __INITIAL_SP              CSTACK$$Limit
+#define __INITIAL_SP              ARM_LIB_STACK$$Limit
 #endif
 
 #ifndef __STACK_LIMIT
-#define __STACK_LIMIT             CSTACK$$Base
+#define __STACK_LIMIT             ARM_LIB_STACK$$Base
 #endif
 
 #ifndef __VECTOR_TABLE