drm: Extend I915 mei interface for transcoder info

I915 needs to send the index of the transcoder as per ME FW.

To support this, define enum mei_fw_tc and add as a member into
the struct hdcp_port_data.

v2:
  Typo in commit msg is fixed [Shashank]
v3:
  kdoc is added for mei_fw_tc [Tomas]
  s/MEI_TC_x/MEI_TRANSCODER_x

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190828164216.405-4-ramalingam.c@intel.com