drm/i915/step: Add macro magic for handling steps

With the addition of stepping info for
all platforms, lets use macros for handling them
and autogenerating code for all steps at a time.

Suggested-by: Matt Roper <matthew.d.roper@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721215238.24980-1-anusha.srivatsa@intel.com