drm/i915/dg2: add DG2+ TRANS_DDI_FUNC_CTL DP 2.0 128b/132b mode

Unfortunately, the DP 2.0 128b/132b DDI mode selection in the register
conflicts with FDI. Since we have to deal with both meanings in the same
code, for different platforms, clarify the macro name so we don't
forget.

Bspec: 50493
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/260e4da302d47ae50122eb8d517be6ac3ccb15f2.1631191763.git.jani.nikula@intel.com