drm/i915/tc: Add an enum for the TypeC pin assignment

drm/i915/tc: Add an enum for the TypeC pin assignment

Add an enum for the TypeC pin assignment, which is a better way to pass
its value around than a plain integer. While at it add a description for
each pin assignment, based on the DP and DP Alt mode Standards, opting
for more details to ease any future debugging related to a given pin
assignment and the cables / sink types used.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
[Imre: s/deined/defined in pin assignment enum documentation.]
Link: https://lore.kernel.org/r/20250805073700.642107-10-imre.deak@intel.com
Signed-off-by: Imre Deak <imre.deak@intel.com>