drm/nv50-nvc0: switch to tasklet for display isr bh

We need to be able to have the bh run while possibly spinning waiting for
the EVO notifier to signal.  This apparently happens in some circumstances
with preempt disabled, so our workqueue was never being run.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nv50_display.h b/drivers/gpu/drm/nouveau/nv50_display.h
index 97d3ed5..ea37f23 100644
--- a/drivers/gpu/drm/nouveau/nv50_display.h
+++ b/drivers/gpu/drm/nouveau/nv50_display.h
@@ -38,6 +38,7 @@
 struct nv50_display {
 	struct nouveau_channel *master;
 
+	struct tasklet_struct tasklet;
 	struct {
 		struct dcb_entry *dcb;
 		u16 script;
@@ -52,7 +53,6 @@
 	return dev_priv->engine.display.priv;
 }
 
-void nv50_display_irq_handler_bh(struct work_struct *work);
 int nv50_display_early_init(struct drm_device *dev);
 void nv50_display_late_takedown(struct drm_device *dev);
 int nv50_display_create(struct drm_device *dev);