csky: VDSO and rt_sigreturn

This patch adds files related to VDSO and our VDSO only support
rt_sigreturn.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>

arch/csky/abiv2/inc/abi/vdso.h

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ABI_CSKY_VDSO_H
+#define __ABI_CSKY_VDSO_H
+
+#include <linux/uaccess.h>
+
+static inline int setup_vdso_page(unsigned short *ptr)
+{
+	int err = 0;
+
+	/* movi r7, 173 */
+	err |= __put_user(0xea07, ptr);
+	err |= __put_user(0x008b,      ptr+1);
+
+	/* trap 0 */
+	err |= __put_user(0xc000,   ptr+2);
+	err |= __put_user(0x2020,   ptr+3);
+
+	return err;
+}
+
+#endif /* __ABI_CSKY_STRING_H */