drm/i915/dg2: Setup display outputs

DG2 has outputs on DDI A-D attached to what the bspec diagram shows as
"Combo PHY A-D."  Note that despite being labelled "combo" the PHYs on
these outputs are Synopsys PHYs rather than traditional Intel combo PHY
technology.

Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721223043.834562-15-matthew.d.roper@intel.com