drm/xe/step: define more steppings E-J

These are primarily needed for compat reasons with display code in
upcoming changes. There's no harm in having them.

While at it, add a comment about the requirement to match against GMD ID
value spacing.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/88074394509d4849f8ec6ab5776394b961032cd0.1724180287.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>