drm/i915/ddi: Unify the platform specific functions disabling a port

The functions disabling a port for MTL+ and earlier platforms only
differ by an extra step on MTL+ (to disable the D2D link) and the point
at which the port's idle state is waited for. Combine the two functions
accounting for the above differences, removing the duplication.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250214142001.552916-10-imre.deak@intel.com