drm/i915/gen9_bc: Introduce HPD pin mappings for TGP PCH + CML combos

Next, let's start introducing the HPD pin mappings for Intel's new gen9_bc
platform in order to make hotplugging display connectors work. Since
gen9_bc is just a TGP PCH along with a CML CPU, except with the same HPD
mappings as ICL, we simply add a skl_hpd_pin function that is shared
between gen9 and gen9_bc which handles both the traditional gen9 HPD pin
mappings and the Icelake HPD pin mappings that gen9_bc uses.

Changes since v4:
* Split this into its own commit
* Introduce skl_hpd_pin() like vsyrjala suggested and use that instead of
  sticking our HPD pin mappings in TGP code

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
[originally from Tejas's work]
Signed-off-by: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@intel.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210209212832.1401815-4-lyude@redhat.com

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

@@ -3954,6 +3954,14 @@ static enum hpd_pin cnl_hpd_pin(struct drm_i915_private *dev_priv,
 	return HPD_PORT_A + port - PORT_A;
 }
 
+static enum hpd_pin skl_hpd_pin(struct drm_i915_private *dev_priv, enum port port)
+{
+	if (HAS_PCH_TGP(dev_priv))
+		return icl_hpd_pin(dev_priv, port);
+
+	return HPD_PORT_A + port - PORT_A;
+}
+
 #define port_tc_name(port) ((port) - PORT_TC1 + '1')
 #define tc_port_name(tc_port) ((tc_port) - TC_PORT_1 + '1')
 
@@ -4070,6 +4078,8 @@ void intel_ddi_init(struct drm_i915_private *dev_priv, enum port port)
 		encoder->hpd_pin = icl_hpd_pin(dev_priv, port);
 	else if (IS_GEN(dev_priv, 10))
 		encoder->hpd_pin = cnl_hpd_pin(dev_priv, port);
+	else if (IS_GEN(dev_priv, 9))
+		encoder->hpd_pin = skl_hpd_pin(dev_priv, port);
 	else
 		encoder->hpd_pin = intel_hpd_pin_default(dev_priv, port);