clk: imx: Move 'imx6sl_set_wait_clk()'s prototype out to accessible header

Fixes the following W=1 kernel build warning(s):

drivers/clk/imx/clk-imx6sl.c:156:6: warning: no previous prototype for ‘imx6sl_set_wait_clk’ [-Wmissing-prototypes]

Cc: Russell King <[e-mail]>
Cc: Shawn Guo <[e-mail]>
Cc: Sascha Hauer <[e-mail]>
Cc: Pengutronix Kernel Team <[e-mail]>
Cc: Fabio Estevam <[e-mail]>
Cc: NXP Linux Team <[e-mail]>
Cc: Ahmad Fatoum <[e-mail]>
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/mach-imx/common.h

···
 void imx_anatop_post_resume(void);
 int imx6_set_lpm(enum mxc_cpu_pwr_mode mode);
 void imx6_set_int_mem_clk_lpm(bool enable);
-void imx6sl_set_wait_clk(bool enter);
 int imx_mmdc_get_ddr_type(void);
 int imx7ulp_set_lpm(enum ulp_cpu_pwr_mode mode);
 

arch/arm/mach-imx/cpuidle-imx6sl.c

···
  * Copyright (C) 2014 Freescale Semiconductor, Inc.
  */
 
+#include <linux/clk/imx.h>
 #include <linux/cpuidle.h>
 #include <linux/module.h>
 #include <asm/cpuidle.h>

arch/arm/mach-imx/pm-imx6.c

···
  * Copyright 2011 Linaro Ltd.
  */
 
+#include <linux/clk/imx.h>
 #include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/io.h>

drivers/clk/imx/clk-imx6sl.c

···
 #include <linux/bits.h>
 #include <linux/clk.h>
 #include <linux/clkdev.h>
+#include <linux/clk/imx.h>
 #include <linux/err.h>
 #include <linux/of.h>
 #include <linux/of_address.h>

include/linux/clk/imx.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 Freescale Semiconductor, Inc.
+ *
+ * Author: Lee Jones <[e-mail]>
+ */
+
+#ifndef __LINUX_CLK_IMX_H
+#define __LINUX_CLK_IMX_H
+
+#include <linux/types.h>
+
+void imx6sl_set_wait_clk(bool enter);
+
+#endif