drm/i915: Use the AUX_IO power domain only for eDP/PSR port

Use the AUX_IO_A display power domain only for eDP on port A where PSR
is also supported. This is the case where DC states need to be enabled
while the output is enabled - ensured by AUX_IO_A domain not enabling
the DC_OFF power well. Otherwise port A can be treated the same way as
other ports with an external DP output: using the AUX_<port> domain
which disables the unrequired DC states.

This change prepares for the next patch enabling DC states on all ports
supporting eDP/PSR besides port A.

v2:
- Check the encoder PSR capability instead of PSR being enabled in the
  crtc_state, as the latter can be changed with a fastset.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221114122251.21327-5-imre.deak@intel.com

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

@@ -862,8 +862,10 @@ intel_ddi_main_link_aux_domain(struct intel_digital_port *dig_port)
 	 * Note that PSR is enabled only on Port A even though this function
 	 * returns the correct domain for other ports too.
 	 */
-	return dig_port->aux_ch == AUX_CH_A ? POWER_DOMAIN_AUX_IO_A :
-					      intel_aux_power_domain(dig_port);
+	if (dig_port->aux_ch == AUX_CH_A && intel_encoder_can_psr(&dig_port->base))
+		return POWER_DOMAIN_AUX_IO_A;
+	else
+		return intel_aux_power_domain(dig_port);
 }
 
 static void intel_ddi_get_power_domains(struct intel_encoder *encoder,