drm/i915/gen12: Add recommended hardware tuning value

Follow Bspec 31870 to set recommended tuning values for certain GT
register.  These values aren't workarounds per-se, but it's best to
handle them in the same general area of the driver, especially since
there may be real workarounds that update other bits of the same
registers.

At the moment the only value we need to worry about is the
TDS_TIMER setting in FF_MODE2.  This setting was previously
described as "Wa_1604555607" on some platforms, but the spec
tells us that we should continue to program this on all current
gen12 platforms, even those that do not have that WA.

Bspec: 31870

v2: Rephrase some comments to make them clearer (Matt)

Cc: Clinton Taylor <clinton.a.taylor@intel.com>
Signed-off-by: Caz Yokoyama <caz.yokoyama@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210324200502.1731265-2-lucas.demarchi@intel.com