drm/i915/fbc: Eliminate possible_framebuffer_bits

Not sure what the point of this fbc->possible_frontbuffer_bits is.
And especially don't see why it's returning all the bits when
fbc is not even enabled. So let's just get rid of this and only
say we are interested in the plane's frontbuffer bits when fbc
is actually enabled.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220315140001.1172-2-ville.syrjala@linux.intel.comReviewed-by: Mika Kahola <mika.kahola@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>

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

@@ -90,7 +90,6 @@ struct intel_fbc {
 	 * with stolen_lock.
 	 */
 	struct mutex lock;
-	unsigned int possible_framebuffer_bits;
 	unsigned int busy_bits;
 
 	struct drm_mm_node compressed_fb;
@@ -1317,7 +1316,7 @@ static unsigned int intel_fbc_get_frontbuffer_bit(struct intel_fbc *fbc)
 	if (fbc->state.plane)
 		return fbc->state.plane->frontbuffer_bit;
 	else
-		return fbc->possible_framebuffer_bits;
+		return 0;
 }
 
 static void __intel_fbc_invalidate(struct intel_fbc *fbc,
@@ -1656,11 +1655,7 @@ static bool need_fbc_vtd_wa(struct drm_i915_private *i915)
 
 void intel_fbc_add_plane(struct intel_fbc *fbc, struct intel_plane *plane)
 {
-	if (!fbc)
-		return;
-
 	plane->fbc = fbc;
-	fbc->possible_framebuffer_bits |= plane->frontbuffer_bit;
 }
 
 static struct intel_fbc *intel_fbc_create(struct drm_i915_private *i915,