drm/i915/icl: Support for TC North Display interrupts

The hotplug interrupts for the ports can be routed to either North
Display or South Display depending on the output mode. DP Alternate or
DP over TBT outputs will have hotplug interrupts routed to the North
Display while interrupts for legacy modes will be routed to the South
Display in PCH. This patch adds hotplug interrupt handling support for
DP Alternate mode.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
[Paulo: coding style changes]
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180616000530.5357-2-paulo.r.zanoni@intel.com