drm/i915/dg2: Program recommended HW settings

The bspec's performance guide suggests programming specific values into
a few registers for optimal performance.  Although these aren't
workarounds, it's easiest to handle them inside the GT workaround
functions (which will also ensure that the values set here are properly
melded with other bits in the same registers that _are_ set by
workarounds).

Bspec: 68331, 45395

Cc: Matt Atwood <matthew.s.atwood@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Siddiqui Ayaz A <ayaz.siddiqui@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Clint Taylor <Clinton.A.Taylor@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211102222511.534310-4-matthew.d.roper@intel.com