csky: Initial stack protector support

This is a basic -fstack-protector support without per-task canary
switching. The protector will report something like when stack
corruption is detected:

It's tested with strcpy local array overflow in sys_kill and get:
stack-protector: Kernel stack is corrupted in: sys_kill+0x23c/0x23c

TODO:
 - Support task switch for different cannary

Signed-off-by: Mao Han <han_mao@c-sky.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>

arch/csky/kernel/process.c

@@ -16,6 +16,12 @@
 
 struct cpuinfo_csky cpu_data[NR_CPUS];
 
+#ifdef CONFIG_STACKPROTECTOR
+#include <linux/stackprotector.h>
+unsigned long __stack_chk_guard __read_mostly;
+EXPORT_SYMBOL(__stack_chk_guard);
+#endif
+
 asmlinkage void ret_from_fork(void);
 asmlinkage void ret_from_kernel_thread(void);