drm/i915/tc: Move TC port fields to a new intel_tc_port struct

Move the TC port specific fields from intel_digital_port to a new
intel_tc_port struct. Pass an intel_tc_port pointer to all static
functions in intel_tc.c keeping dig_port accessible for these via a
pointer stored in the new struct.

The next patch will allocate the intel_tc_port dynamically, allowing
moving the struct definition to intel_tc.c.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323142035.1432621-6-imre.deak@intel.com