drm/i915/tc: Pass pin assignment value around using the pin assignment enum

drm/i915/tc: Pass pin assignment value around using the pin assignment enum

Pass around the pin assignment value via the corresponding enum instead
of a plain integer.

While at it rename intel_tc_port_get_pin_assignment_mask() to
intel_tc_port_get_pin_assignment(), since the value returned is not a
mask.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://lore.kernel.org/r/20250805073700.642107-11-imre.deak@intel.com
Signed-off-by: Imre Deak <imre.deak@intel.com>