dg2_ddi_pre_enable_dp() has outlived its usefulness so eliminate
it.

The one thing that tgl_ddi_pre_enable_dp() is missing that we
need is intel_ddi_config_transcoder_dp2(). So we'll bring that
over.

tgl_ddi_pre_enable_dp() does also have a few things that
dg2_ddi_pre_enable_dp() didn't have:
- icl_program_mg_dp_mode() -> nop due to intel_phy_is_tc()==false on DG2
- intel_ddi_power_up_lanes() -> nop due to intel_phy_is_combo()==false on DG2
- intel_ddi_mso_configure() -> only matters for MSO panels

Another slight difference is that dg2_ddi_pre_enable_dp() was
missing a bigjoiner check around intel_dsc_enable(), which
tgl_ddi_pre_enable_dp() does have.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220119122150.12941-1-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>