drm/i915: Use enum plane_id for frontbuffer tracking

Replace the ad-hoc plane indexing scheme used by the frontbuffer
tracking with enum plane_id.

The old video overlay not being part of the plane_id namespace
will just be given the high bit.

v2: Drop the unintended whitespace change (Chris)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180123183343.9181-1-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index 9dc2b8b..a8a8a80 100644
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -1373,7 +1373,7 @@ void intel_fbc_init(struct drm_i915_private *dev_priv)
 
 	for_each_pipe(dev_priv, pipe) {
 		fbc->possible_framebuffer_bits |=
-				INTEL_FRONTBUFFER_PRIMARY(pipe);
+			INTEL_FRONTBUFFER(pipe, PLANE_PRIMARY);
 
 		if (fbc_on_pipe_a_only(dev_priv))
 			break;