HID: multitouch: Set to high latency mode on suspend.

Per Windows Precision Touchpad guidelines:

> The latency mode feature report is sent by the host to a Windows
> Precision Touchpad to indicate when high latency is desirable for
> power savings and, conversely, when normal latency is desired for
> operation.
>
> For USB-connected Windows Precision Touchpads, this enables the device
> to disambiguate between being suspended for inactivity (runtime IDLE)
> and being suspended because the system is entering S3 or Connected
> Standby.

The current implementation would set the latency to normal on device initialization,
but we didn't set the device to high latency on suspend.

Signed-off-by: Blaž Hrastnik <[e-mail]>
Acked-by: Benjamin Tissoires <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

drivers/hid/hid-multitouch.c

···
 }
 
 #ifdef CONFIG_PM
+static int mt_suspend(struct hid_device *hdev, pm_message_t state)
+{
+	/* High latency is desirable for power savings during S3/S0ix */
+	mt_set_modes(hdev, HID_LATENCY_HIGH, true, true);
+	return 0;
+}
+
 static int mt_reset_resume(struct hid_device *hdev)
 {
 	mt_release_contacts(hdev);
···
 	 * Tested on 3M, Stantum, Cypress, Zytronic, eGalax, and Elan panels. */
 
 	hid_hw_idle(hdev, 0, 0, HID_REQ_SET_IDLE);
+
+	mt_set_modes(hdev, HID_LATENCY_NORMAL, true, true);
 
 	return 0;
 }
···
 	.event = mt_event,
 	.report = mt_report,
 #ifdef CONFIG_PM
+	.suspend = mt_suspend,
 	.reset_resume = mt_reset_resume,
 	.resume = mt_resume,
 #endif