drm/i915: Introduce intel_plane_state_reset()

For the sake of symmetry with the crtc stuff let's add
a helper to reset the plane state to sane default values.
For the moment this only gets caller from the plane init.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191107142417.11107-5-ville.syrjala@linux.intel.comReviewed-by: NJosé Roberto de Souza <jose.souza@intel.com>

drivers/gpu/drm/i915/display/intel_atomic_plane.c

@@ -41,6 +41,16 @@
 #include "intel_pm.h"
 #include "intel_sprite.h"
 
+static void intel_plane_state_reset(struct intel_plane_state *plane_state,
+				    struct intel_plane *plane)
+{
+	memset(plane_state, 0, sizeof(*plane_state));
+
+	__drm_atomic_helper_plane_state_reset(&plane_state->uapi, &plane->base);
+
+	plane_state->scaler_id = -1;
+}
+
 struct intel_plane *intel_plane_alloc(void)
 {
 	struct intel_plane_state *plane_state;
@@ -56,8 +66,9 @@ struct intel_plane *intel_plane_alloc(void)
 		return ERR_PTR(-ENOMEM);
 	}
 
-	__drm_atomic_helper_plane_reset(&plane->base, &plane_state->uapi);
-	plane_state->scaler_id = -1;
+	intel_plane_state_reset(plane_state, plane);
+
+	plane->base.state = &plane_state->uapi;
 
 	return plane;
 }