drm/i915: Make encoder cloning more flexible

Currently we allow encoders to indicate whether they can be part of a
cloned set with just one flag. That's not flexible enough to describe
the actual hardware capabilities. Instead make it a bitmask of encoder
types with which the current encoder can be cloned.

For now we set the bitmask to allow DVO+DVO and DVO+VGA, which should
match what the old boolean flag allowed. We will add some more cloning
options in the future.

Note that this patch also removes the encoder.possible_clones setting
from encoder setup code - we compute this dynamically.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
[danvet: Add Ville's explanation why removing the encoder
possible_clones is save.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_drv.h

@@ -125,11 +125,7 @@ struct intel_encoder {
 	struct intel_crtc *new_crtc;
 
 	int type;
-	/*
-	 * Intel hw has only one MUX where encoders could be clone, hence a
-	 * simple flag is enough to compute the possible_clones mask.
-	 */
-	bool cloneable;
+	unsigned int cloneable;
 	bool connectors_active;
 	void (*hot_plug)(struct intel_encoder *);
 	bool (*compute_config)(struct intel_encoder *,