drm/i915/dg2: Don't program BW_BUDDY registers

Although the BW_BUDDY registers still exist, they are not used for
anything on DG2.  This change is expected to hold true for future dgpu's
too.

Bspec: 49218
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/20210721223043.834562-17-matthew.d.roper@intel.com