reset: sunxi: declare sun6i_reset_init in a header file

Avoid declaring extern functions in c files. To make sure function
definition and usage don't get out of sync, declare sun6i_reset_init
in a common header.

Suggested-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

include/linux/reset/sunxi.h

@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_RESET_SUNXI_H__
+#define __LINUX_RESET_SUNXI_H__
+
+void __init sun6i_reset_init(void);
+
+#endif /* __LINUX_RESET_SUNXI_H__ */