Add INIT_ATTR to system_init()

On single-core targets, system_init() is only called from init()
in main.c, which is also INIT_ATTR, so this is safe.

Multi-core targets additionally call system_init() from cop_main(),
which isn't marked INIT_ATTR. I'm fairly certain that it would be
safe to add INIT_ATTR to cop_main() with a bit of refactoring, but
I don't have a way of testing it. So for now, leave INIT_ATTR off
for multi-core targets.

Change-Id: I8fe4358f975880ca317d46bda01d7d9db529d3e3

firmware/export/system.h

@@ -31,7 +31,13 @@ extern void system_reboot (void);
 /* Called from any UIE handler and panicf - wait for a key and return
  * to reboot system. */
 extern void system_exception_wait(void);
+
+#if NUM_CORES == 1
+extern void system_init(void) INIT_ATTR;
+#else
+/* TODO: probably safe to use INIT_ATTR on multicore but this needs checking */
 extern void system_init(void);
+#endif
 
 extern long cpu_frequency;
 

firmware/target/arm/imx31/gigabeat-s/system-gigabeat-s.c

@@ -199,7 +199,7 @@ void system_exception_wait(void)
     system_halt();
 }
 
-void INIT_ATTR system_init(void)
+void system_init(void)
 {
     static const enum IMX31_CG_LIST disable_clocks[] INITDATA_ATTR =
     {