drm/udl: implement usb_driver suspend/resume.

The usb_driver suspend and resume function pointers must be populated
to prevent forced unbinding of USB interface driver. See usb/core/driver.c:
unbind_no_pm_drivers_interfaces().

Restore mode and damage the entire frame buffer upon resume.

TEST=suspend and resume with the same UDL device connected
TEST=suspend with UDL, unplug UDL and resume
TEST=suspend with UDL, unplug and connect another UDL device then resume

Signed-off-by: Haixia Shi <hshi@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
[seanpaul fixed checkpatch warnings and gave marcheu his é back]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1472593821-38429-2-git-send-email-hshi@chromium.org
diff --git a/drivers/gpu/drm/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
index 17d34e0..f0851db 100644
--- a/drivers/gpu/drm/udl/udl_drv.c
+++ b/drivers/gpu/drm/udl/udl_drv.c
@@ -16,6 +16,20 @@
 	return 0;
 }
 
+static int udl_usb_suspend(struct usb_interface *interface,
+			   pm_message_t message)
+{
+	return 0;
+}
+
+static int udl_usb_resume(struct usb_interface *interface)
+{
+	struct drm_device *dev = usb_get_intfdata(interface);
+
+	udl_modeset_restore(dev);
+	return 0;
+}
+
 static const struct vm_operations_struct udl_gem_vm_ops = {
 	.fault = udl_gem_fault,
 	.open = drm_gem_vm_open,
@@ -122,6 +136,8 @@
 	.name = "udl",
 	.probe = udl_usb_probe,
 	.disconnect = udl_usb_disconnect,
+	.suspend = udl_usb_suspend,
+	.resume = udl_usb_resume,
 	.id_table = id_table,
 };
 module_usb_driver(udl_driver);