drm/i915/icl: Set TC type to unknown in the disconnection flow

Otherwise it would be in a inconsistent state as port is disconnected
but with a valid tc type.

Also setting it to unknown will earlier return
icl_tc_phy_disconnect() for any future calls to
intel_digital_port_connected(), this way we don't need to check if
port is marked as safe everytime.

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181030215750.28213-2-jose.souza@intel.com