drm/nouveau: set irq_enabled manually

Since commit 0fa9061ae8 ("drm/nouveau/mc: handle irq-related setup
ourselves"), drm_device->irq_enabled remained unset. This is needed in
order to properly wait for a vblank event in the generic drm code.

See https://bugs.freedesktop.org/show_bug.cgi?id=74195

Reported-by: Jan Janecek <janjanjanx@gmail.com>
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_drm.c

@@ -376,6 +376,8 @@ nouveau_drm_load(struct drm_device *dev, unsigned long flags)
 	if (ret)
 		goto fail_device;
 
+	dev->irq_enabled = true;
+
 	/* workaround an odd issue on nvc1 by disabling the device's
 	 * nosnoop capability.  hopefully won't cause issues until a
 	 * better fix is found - assuming there is one...
@@ -475,6 +477,7 @@ nouveau_drm_remove(struct pci_dev *pdev)
 	struct nouveau_drm *drm = nouveau_drm(dev);
 	struct nouveau_object *device;
 
+	dev->irq_enabled = false;
 	device = drm->client.base.device;
 	drm_put_dev(dev);