Add some debugging so I can see when syscalls are being restarted

consistantly.  After a lengthy irc discussion it seems like we
shouldn't need to worry about them, but it's nice to know about.

MFC after:	3 days

sys/dev/drm/drm_lock.c

@@ -87,7 +87,12 @@ int drm_lock(struct drm_device *dev, void *data, struct drm_file *file_priv)
 			break;
 	}
 	DRM_UNLOCK();
-	DRM_DEBUG("%d %s\n", lock->context, ret ? "interrupted" : "has lock");
+
+	if (ret == ERESTART)
+		DRM_DEBUG("restarting syscall\n");
+	else
+		DRM_DEBUG("%d %s\n", lock->context,
+		    ret ? "interrupted" : "has lock");
 
 	if (ret != 0)
 		return ret;

sys/dev/drm/mga_irq.c

@@ -139,6 +139,9 @@ int mga_driver_fence_wait(struct drm_device * dev, unsigned int *sequence)
 		    (((cur_fence = atomic_read(&dev_priv->last_fence_retired))
 		      - *sequence) <= (1 << 23)));
 
+	if (ret == -ERESTART)
+		DRM_DEBUG("restarting syscall\n");
+
 	*sequence = cur_fence;
 
 	return ret;

sys/dev/drm/radeon_irq.c

@@ -282,6 +282,9 @@ static int radeon_wait_irq(struct drm_device * dev, int swi_nr)
 	DRM_WAIT_ON(ret, dev_priv->swi_queue, 3 * DRM_HZ,
 		    RADEON_READ(RADEON_LAST_SWI_REG) >= swi_nr);
 
+	if (ret == -ERESTART)
+		DRM_DEBUG("restarting syscall");
+
 	return ret;
 }