drm/i915/ddi: enable 128b/132b TRANS_DDI_FUNC_CTL mode for UHBR SST

128b/132b SST needs 128b/132b mode enabled in the TRANS_DDI_FUNC_CTL
register.

This is preparation for enabling 128b/132b SST. This path is not
reachable yet.

v2: Use the MST path instead of SST to also set transport select (Imre)

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/122ebeadf4bf0870fc26b7d12abdff88f4be8799.1735912293.git.jani.nikula@intel.com