MLK-21076-7 pinctrl: imx8mn: Fix build warning when CONFIG_PM_SLEEP=n

MLK-21076-7 pinctrl: imx8mn: Fix build warning when CONFIG_PM_SLEEP=n

Fix below build warning when CONFIG_PM_SLEEP=n:

drivers/pinctrl/freescale/pinctrl-imx8mn.c:355:12: warning:
 ‘imx8mn_pinctrl_suspend’ defined but not used [-Wunused-function]
 static int imx8mn_pinctrl_suspend(struct device *dev)
            ^
drivers/pinctrl/freescale/pinctrl-imx8mn.c:360:12: warning:
 ‘imx8mn_pinctrl_resume’ defined but not used [-Wunused-function]
 static int imx8mn_pinctrl_resume(struct device *dev)
            ^

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Jacky Bai <ping.bai@nxp.com>
(cherry picked from commit 6f84c2d2d1e30d8f3cf68245fa1f12dfac8b6a8e)