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 <[e-mail]>
Signed-off-by: Philipp Zabel <[e-mail]>

arch/arm/mach-sunxi/sunxi.c

···
 #include <linux/clocksource.h>
 #include <linux/init.h>
 #include <linux/platform_device.h>
+#include <linux/reset/sunxi.h>
 
 #include <asm/mach/arch.h>
 #include <asm/secure_cntvoff.h>
···
 	NULL,
 };
 
-extern void __init sun6i_reset_init(void);
 static void __init sun6i_timer_init(void)
 {
 	of_clk_init(NULL);

drivers/reset/reset-sunxi.c

···
 #include <linux/of_address.h>
 #include <linux/platform_device.h>
 #include <linux/reset-controller.h>
+#include <linux/reset/sunxi.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/types.h>

include/linux/reset/sunxi.h

···
+/* 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__ */