platform/surface: surface_gpe: Fix non-PM_SLEEP build warnings

Fix build warnings when CONFIG_PM_SLEEP is not enabled and these
functions are not used:

../drivers/platform/surface/surface_gpe.c:189:12: warning: ‘surface_gpe_resume’ defined but not used [-Wunused-function]
 static int surface_gpe_resume(struct device *dev)
            ^~~~~~~~~~~~~~~~~~
../drivers/platform/surface/surface_gpe.c:184:12: warning: ‘surface_gpe_suspend’ defined but not used [-Wunused-function]
 static int surface_gpe_suspend(struct device *dev)
            ^~~~~~~~~~~~~~~~~~~

Fixes: 274335f1 ("platform/surface: Add Driver to set up lid GPEs on MS Surface device")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Maximilian Luz <luzmaximilian@gmail.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: platform-driver-x86@vger.kernel.org
Reviewed-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20201214233336.19782-1-rdunlap@infradead.orgSigned-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/surface/surface_gpe.c

@@ -181,12 +181,12 @@ static int surface_lid_enable_wakeup(struct device *dev, bool enable)
 	return 0;
 }
 
-static int surface_gpe_suspend(struct device *dev)
+static int __maybe_unused surface_gpe_suspend(struct device *dev)
 {
 	return surface_lid_enable_wakeup(dev, true);
 }
 
-static int surface_gpe_resume(struct device *dev)
+static int __maybe_unused surface_gpe_resume(struct device *dev)
 {
 	return surface_lid_enable_wakeup(dev, false);
 }