ACPI / PM: Fix unused function warnings for CONFIG_PM_SLEEP

According to compiler warnings, several suspend/resume functions
in ACPI drivers are not used for CONFIG_PM_SLEEP unset, so add
#ifdefs to prevent them from being built in that case.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/drivers/acpi/ac.c b/drivers/acpi/ac.c
index ac70341..d5fdd36 100644
--- a/drivers/acpi/ac.c
+++ b/drivers/acpi/ac.c
@@ -69,7 +69,9 @@
 };
 MODULE_DEVICE_TABLE(acpi, ac_device_ids);
 
+#ifdef CONFIG_PM_SLEEP
 static int acpi_ac_resume(struct device *dev);
+#endif
 static SIMPLE_DEV_PM_OPS(acpi_ac_pm, NULL, acpi_ac_resume);
 
 static struct acpi_driver acpi_ac_driver = {
@@ -313,6 +315,7 @@
 	return result;
 }
 
+#ifdef CONFIG_PM_SLEEP
 static int acpi_ac_resume(struct device *dev)
 {
 	struct acpi_ac *ac;
@@ -332,6 +335,7 @@
 		kobject_uevent(&ac->charger.dev->kobj, KOBJ_CHANGE);
 	return 0;
 }
+#endif
 
 static int acpi_ac_remove(struct acpi_device *device, int type)
 {