drm/i915: mei_hdcp: I915 sends ddi index as per ME FW

I915 converts it's port value into ddi index defiend by ME FW
and pass it as a member of hdcp_port_data structure.

Hence expose the enum mei_fw_ddi to I915 through
i915_mei_interface.h.

v2:
  Copyright years are bumped [Tomas]

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Acked-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190828164216.405-2-ramalingam.c@intel.com