mfd: intel-lpss: Hide suspend/resume functions in #ifdef

When CONFIG_PM is disabled, the prototypes for these two functions
are not visible:

drivers/mfd/intel-lpss.c:482:5: error: no previous prototype for 'intel_lpss_suspend' [-Werror=missing-prototypes]
  482 | int intel_lpss_suspend(struct device *dev)
      |     ^~~~~~~~~~~~~~~~~~
drivers/mfd/intel-lpss.c:503:5: error: no previous prototype for 'intel_lpss_resume' [-Werror=missing-prototypes]
  503 | int intel_lpss_resume(struct device *dev)

Add the same #ifdef around the definition of the unused functions,
which avoids the warning and slightly reduces the code size.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230516202746.561111-1-arnd@kernel.orgSigned-off-by: Lee Jones <lee@kernel.org>

drivers/mfd/intel-lpss.c

@@ -460,6 +460,7 @@ void intel_lpss_remove(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(intel_lpss_remove);
 
+#ifdef CONFIG_PM
 static int resume_lpss_device(struct device *dev, void *data)
 {
 	if (!dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND))
@@ -514,6 +515,7 @@ int intel_lpss_resume(struct device *dev)
 	return 0;
 }
 EXPORT_SYMBOL_GPL(intel_lpss_resume);
+#endif
 
 static int __init intel_lpss_init(void)
 {