drm/i915/display: For MTL+ platforms skip mg dp programming

For MTL+ platforms we use PICA chips for Type-C support and
hence mg programming is not needed.

Fixes issue with drm warn of TC port not being in legacy mode.

Cc: stable@vger.kernel.org

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240625111840.597574-1-mika.kahola@intel.com
(cherry picked from commit aaf9dc86

)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>