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/sbs.c b/drivers/acpi/sbs.c
index c0b9aa5..ff0740e 100644
--- a/drivers/acpi/sbs.c
+++ b/drivers/acpi/sbs.c
@@ -988,6 +988,7 @@
 #endif
 }
 
+#ifdef CONFIG_PM_SLEEP
 static int acpi_sbs_resume(struct device *dev)
 {
 	struct acpi_sbs *sbs;
@@ -997,6 +998,7 @@
 	acpi_sbs_callback(sbs);
 	return 0;
 }
+#endif
 
 static SIMPLE_DEV_PM_OPS(acpi_sbs_pm, NULL, acpi_sbs_resume);