drm/i915/skl: Introduce intel_num_planes()

It can be handy to get the number of planes for this pipe, ie including
the primary plane to loop over them. Introduce a little function to do
so.
Reviewed-by: NRodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_drv.h

@@ -731,6 +731,14 @@ hdmi_to_dig_port(struct intel_hdmi *intel_hdmi)
 	return container_of(intel_hdmi, struct intel_digital_port, hdmi);
 }
 
+/*
+ * Returns the number of planes for this pipe, ie the number of sprites + 1
+ * (primary plane). This doesn't count the cursor plane then.
+ */
+static inline unsigned int intel_num_planes(struct intel_crtc *crtc)
+{
+	return INTEL_INFO(crtc->base.dev)->num_sprites[crtc->pipe] + 1;
+}
 
 /* i915_irq.c */
 bool intel_set_cpu_fifo_underrun_reporting(struct drm_device *dev,