drm/i915/icl: Add allowed DP rates for Icelake

For ICL, on Combo PHY the allowed max rates are:
 - HBR3 8.1 eDP (DDIA)
 - HBR2 5.4 DisplayPort (DDIB)
and for MG PHY/TC DDI Ports allowed DP rates are:
 - HBR3 8.1 DisplayPort (DP alternate mode, DP over TBT,
 - DP on legacy connector - DDIC/D/E/F)

v2 (from Paulo): Remove misleading comment (Ville).

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: James Ausmus <james.ausmus@intel.com>
[Paulo: bikeshed to keep future platforms on "else", v2.]
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180611222655.5696-1-paulo.r.zanoni@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -256,6 +256,17 @@ static int cnl_max_source_rate(struct intel_dp *intel_dp)
 	return 810000;
 }
 
+static int icl_max_source_rate(struct intel_dp *intel_dp)
+{
+	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
+	enum port port = dig_port->base.port;
+
+	if (port == PORT_B)
+		return 540000;
+
+	return 810000;
+}
+
 static void
 intel_dp_set_source_rates(struct intel_dp *intel_dp)
 {
@@ -285,10 +296,13 @@ intel_dp_set_source_rates(struct intel_dp *intel_dp)
 	/* This should only be done once */
 	WARN_ON(intel_dp->source_rates || intel_dp->num_source_rates);
 
-	if (IS_CANNONLAKE(dev_priv)) {
+	if (INTEL_GEN(dev_priv) >= 10) {
 		source_rates = cnl_rates;
 		size = ARRAY_SIZE(cnl_rates);
-		max_rate = cnl_max_source_rate(intel_dp);
+		if (INTEL_GEN(dev_priv) == 10)
+			max_rate = cnl_max_source_rate(intel_dp);
+		else
+			max_rate = icl_max_source_rate(intel_dp);
 	} else if (IS_GEN9_LP(dev_priv)) {
 		source_rates = bxt_rates;
 		size = ARRAY_SIZE(bxt_rates);