drm/i915/dg2: Skip shared DPLL handling

DG2 has no shared DPLL's or DDI clock muxing.  The Port PLL is embedded
within the PHY.

Bspec: 54032
Bspec: 54034
Cc: Lucas De Marchi <lucas.demarchi@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/20210721223043.834562-13-matthew.d.roper@intel.com