drm/i915/bxt: Use correct live status register for BXT platform

BXT platform uses live status bits from 0x44440 register to obtain DP
status on hotplug. The existing g4x_digital_port_connected() uses a
different register and hence misses DP hotplug events on BXT
platform. This patch fixes it by using the appropriate register(0x44440)
and live status bits(3:5).

Based on a patch by Durgadoss R <durgadoss.r@intel.com>, from whom the
commit message is shamelessly copy pasted.

Reported-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -4576,6 +4576,29 @@ static bool vlv_digital_port_connected(struct drm_i915_private *dev_priv,
 	return I915_READ(PORT_HOTPLUG_STAT) & bit;
 }
 
+static bool bxt_digital_port_connected(struct drm_i915_private *dev_priv,
+				       struct intel_digital_port *port)
+{
+	u32 bit;
+
+	switch (port->port) {
+	case PORT_A:
+		bit = BXT_DE_PORT_HP_DDIA;
+		break;
+	case PORT_B:
+		bit = BXT_DE_PORT_HP_DDIB;
+		break;
+	case PORT_C:
+		bit = BXT_DE_PORT_HP_DDIC;
+		break;
+	default:
+		MISSING_CASE(port->port);
+		return false;
+	}
+
+	return I915_READ(GEN8_DE_PORT_ISR) & bit;
+}
+
 /*
  * intel_digital_port_connected - is the specified port connected?
  * @dev_priv: i915 private structure
@@ -4590,6 +4613,8 @@ static bool intel_digital_port_connected(struct drm_i915_private *dev_priv,
 		return ibx_digital_port_connected(dev_priv, port);
 	if (HAS_PCH_SPLIT(dev_priv))
 		return cpt_digital_port_connected(dev_priv, port);
+	else if (IS_BROXTON(dev_priv))
+		return bxt_digital_port_connected(dev_priv, port);
 	else if (IS_VALLEYVIEW(dev_priv))
 		return vlv_digital_port_connected(dev_priv, port);
 	else