drm/i915: Use alphabetical names for sprites

Add sprite_name() macro which should be used with the kind of sprites
that are fixed to pipes (gen4.5+).

Also use dev_priv->num_plane to calculate the sprite index insted
assuming two sprites per pipe. This should make it print the right
name.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d5dcf7f..15d0a3a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -76,6 +76,8 @@
 };
 #define plane_name(p) ((p) + 'A')
 
+#define sprite_name(p, s) ((p) * dev_priv->num_plane + (s) + 'A')
+
 enum port {
 	PORT_A = 0,
 	PORT_B,