drm/i915: add MISSING_CASE to a few port/aux power domain helpers

MISSING_CASE() would have been useful to track down a recent problem in
intel_display_port_aux_power_domain(), so add it there and a few related
helpers. This was also suggested by Ville in his review of the latest
DMC/DC changes, we forgot to address that.
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPatrik Jakobsson <patrik.jakobsson@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1447855045-7109-2-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -5177,7 +5177,7 @@ static enum intel_display_power_domain port_to_power_domain(enum port port)
 	case PORT_E:
 		return POWER_DOMAIN_PORT_DDI_E_LANES;
 	default:
-		WARN_ON_ONCE(1);
+		MISSING_CASE(port);
 		return POWER_DOMAIN_PORT_OTHER;
 	}
 }
@@ -5197,7 +5197,7 @@ static enum intel_display_power_domain port_to_aux_power_domain(enum port port)
 		/* FIXME: Check VBT for actual wiring of PORT E */
 		return POWER_DOMAIN_AUX_D;
 	default:
-		WARN_ON_ONCE(1);
+		MISSING_CASE(port);
 		return POWER_DOMAIN_AUX_A;
 	}
 }
@@ -5258,7 +5258,7 @@ intel_display_port_aux_power_domain(struct intel_encoder *intel_encoder)
 		intel_dig_port = enc_to_mst(&intel_encoder->base)->primary;
 		return port_to_aux_power_domain(intel_dig_port->port);
 	default:
-		WARN_ON_ONCE(1);
+		MISSING_CASE(intel_encoder->type);
 		return POWER_DOMAIN_AUX_A;
 	}
 }