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: 274335f1c557 ("platform/surface: Add Driver to set up lid GPEs on MS Surface device")
Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Maximilian Luz <[e-mail]>
Cc: Hans de Goede <[e-mail]>
Cc: [e-mail]
Reviewed-by: Maximilian Luz <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Hans de Goede <[e-mail]>

drivers/platform/surface/surface_gpe.c

···
 	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);
 }