drm/i915: s/PORT_TC/TC_PORT_/

Make the namespacing for enum tc_port better by adding
the TC_ to the actual enum values.

v2: Drop the extra TC (Lucas)

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201028213323.5423-2-ville.syrjala@linux.intel.com