drm/i915/glk: Use revid->stepping tables

Switch GLK to use a revid->stepping table as we're trying to do on all
platforms going forward.  Pre-production and placeholder revisions are
omitted.

Although nothing in the code is using the data from this table at the
moment, we expect some upcoming DMC patches to start utilizing it.

Bspec: 19131
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210713193635.3390052-7-matthew.d.roper@intel.com