drm/i915/display: Program DBUF_CTL tracker state service

This sequence is not part of "Sequences to Initialize Display" but
as noted in the MBus page the DBUF_CTL.Tracker_state_service needs
to be set to 8.

BSpec: 49213
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201019173906.18892-1-jose.souza@intel.com