drm/i915: Use enum i9xx_plane_id for the .get_fifo_size() hooks

Replace the 0 and 1 with PLANE_A and PLANE_B in the pre-g4x wm code.

v2: s/old_plane_id/i9xx_plane_id/ (Daniel)
v3: s/plane/i9xx_plane/ etc. (James)

Cc: James Ausmus <james.ausmus@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171117191917.11506-5-ville.syrjala@linux.intel.com
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d63a731..a1268d7 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -698,7 +698,8 @@ struct drm_i915_display_funcs {
 			  struct intel_cdclk_state *cdclk_state);
 	void (*set_cdclk)(struct drm_i915_private *dev_priv,
 			  const struct intel_cdclk_state *cdclk_state);
-	int (*get_fifo_size)(struct drm_i915_private *dev_priv, int plane);
+	int (*get_fifo_size)(struct drm_i915_private *dev_priv,
+			     enum i9xx_plane_id i9xx_plane);
 	int (*compute_pipe_wm)(struct intel_crtc_state *cstate);
 	int (*compute_intermediate_wm)(struct drm_device *dev,
 				       struct intel_crtc *intel_crtc,