drm/i915/dg2: Configure PCON in DP pre-enable path

Add the functions to configure HDMI2.1 pcon for DG2, before DP link
training.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@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/20210805163647.801064-10-matthew.d.roper@intel.com