drm/i915/dg1: Use revid->stepping tables

Switch DG1 to use a revid->stepping table as we're trying to do on all
platforms going forward.

This removes the last use of IS_REVID() and REVID_FOREVER, so remove
those now-unused macros as well to prevent their accidental use on
future platforms.

v2:
 - Use COMMON_STEP() macro in table.  (Anusha)

Bspec: 44463
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/20210713193635.3390052-11-matthew.d.roper@intel.com