drm/i915/gt: Add dedicated function for non-ctx register tuning settings

The bspec performance tuning section gives recommended settings that the
driver should program for various MMIO registers.  Although these
settings aren't "workarounds" we use the workaround infrastructure to do
this programming to make sure it is handled at the appropriate places
and doesn't conflict with any real workarounds.

Since more of these are starting to show up on recent platforms, it's a
good time to create a dedicated function to hold them so that there's
less ambiguity about how/where to implement new ones.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220816210601.2041572-1-matthew.d.roper@intel.com