Bluetooth: btnxpuart: Fix warnings for suspend and resume functions

This fixes the warnings 'nxp_serdev_resume' and 'nxp_serdev_suspend'
defined but not used.
Signed-off-by: Neeraj Sanjay Kale <neeraj.sanjaykale@nxp.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202407100518.06Xxq5PK-lkp@intel.com/Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

drivers/bluetooth/btnxpuart.c

@@ -1522,6 +1522,7 @@ static void nxp_serdev_remove(struct serdev_device *serdev)
 	hci_free_dev(hdev);
 }
 
+#ifdef CONFIG_PM_SLEEP
 static int nxp_serdev_suspend(struct device *dev)
 {
 	struct btnxpuart_dev *nxpdev = dev_get_drvdata(dev);
@@ -1539,6 +1540,7 @@ static int nxp_serdev_resume(struct device *dev)
 	ps_control(psdata->hdev, PS_STATE_AWAKE);
 	return 0;
 }
+#endif
 
 static struct btnxpuart_data w8987_data __maybe_unused = {
 	.helper_fw_name = NULL,