scsi: ufs: ufs-mediatek: Guard power management functions with CONFIG_PM

Fix the following compilation error when CONFIG_PM is set to 'n':

drivers/ufs/host/ufs-mediatek.c: In function `ufs_mtk_runtime_suspend`:
drivers/ufs/host/ufs-mediatek.c:1623:8: error: implicit declaration of
	function `ufshcd_runtime_suspend`; did you mean `ufs_mtk_runtime_suspend`?
	[-Werror=implicit-function-declaration]
 1623 |  ret = ufshcd_runtime_suspend(dev);
      |        ^~~~~~~~~~~~~~~~~~~~~~
      |        ufs_mtk_runtime_suspend
drivers/ufs/host/ufs-mediatek.c: In function `ufs_mtk_runtime_resume`:
drivers/ufs/host/ufs-mediatek.c:1638:9: error: implicit declaration of function
	`ufshcd_runtime_resume`; did you mean `ufs_mtk_runtime_resume`?
	[-Werror=implicit-function-declaration]
 1638 |  return ufshcd_runtime_resume(dev);
      |         ^~~~~~~~~~~~~~~~~~~~~
      |         ufs_mtk_runtime_resume
At top level:
drivers/ufs/host/ufs-mediatek.c:1632:12: error: `ufs_mtk_runtime_resume`
	defined but not used [-Werror=unused-function]
 1632 | static int ufs_mtk_runtime_resume(struct device *dev)
      |            ^~~~~~~~~~~~~~~~~~~~~~
drivers/ufs/host/ufs-mediatek.c:1618:12: error: `ufs_mtk_runtime_suspend`
	defined but not used [-Werror=unused-function]
 1618 | static int ufs_mtk_runtime_suspend(struct device *dev)

Link: https://lore.kernel.org/r/20230220142431.54589-1-frank.li@vivo.com
Reported-by: k2ci <kernel-bot@kylinos.cn>
Reported-by: Shida Zhang <zhangshida@kylinos.cn>
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/ufs/host/ufs-mediatek.c

@@ -1613,6 +1613,7 @@ static int ufs_mtk_system_resume(struct device *dev)
 }
 #endif
 
+#ifdef CONFIG_PM
 static int ufs_mtk_runtime_suspend(struct device *dev)
 {
 	struct ufs_hba *hba = dev_get_drvdata(dev);
@@ -1635,6 +1636,7 @@ static int ufs_mtk_runtime_resume(struct device *dev)
 
 	return ufshcd_runtime_resume(dev);
 }
+#endif
 
 static const struct dev_pm_ops ufs_mtk_pm_ops = {
 	SET_SYSTEM_SLEEP_PM_OPS(ufs_mtk_system_suspend,