drm/i915: Introduce intel_hpd_pin function.

The idea is to have an unique place to decide the pin-port
per platform.

So let's create this function now without any functional
change. Just adding together code from hdmi and dp together.

v2: Add missing pin for port A.
v3: Fix typo on subject.
    Avoid behaviour change so add WARN_ON and return
    if port A on HDMI. (by DK).

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170811182650.14327-2-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -5916,26 +5916,22 @@ intel_dp_init_connector_port_info(struct intel_digital_port *intel_dig_port)
 	struct intel_encoder *encoder = &intel_dig_port->base;
 	struct intel_dp *intel_dp = &intel_dig_port->dp;
 
+	encoder->hpd_pin = intel_hpd_pin(intel_dig_port->port);
+
 	switch (intel_dig_port->port) {
 	case PORT_A:
-		encoder->hpd_pin = HPD_PORT_A;
 		intel_dp->aux_power_domain = POWER_DOMAIN_AUX_A;
 		break;
 	case PORT_B:
-		encoder->hpd_pin = HPD_PORT_B;
 		intel_dp->aux_power_domain = POWER_DOMAIN_AUX_B;
 		break;
 	case PORT_C:
-		encoder->hpd_pin = HPD_PORT_C;
 		intel_dp->aux_power_domain = POWER_DOMAIN_AUX_C;
 		break;
 	case PORT_D:
-		encoder->hpd_pin = HPD_PORT_D;
 		intel_dp->aux_power_domain = POWER_DOMAIN_AUX_D;
 		break;
 	case PORT_E:
-		encoder->hpd_pin = HPD_PORT_E;
-
 		/* FIXME: Check VBT for actual wiring of PORT E */
 		intel_dp->aux_power_domain = POWER_DOMAIN_AUX_D;
 		break;