drm/xe: Upgrade complaint about missing slice info

The steering code needs to know slice/subslice counts and this
information should be retrieved from the hwconfig table. However,
earlier platforms don't have it, hence the KMD has a fallback path.
Newer platforms really should have the entries and if they are missing
that is a bug that needs to be fixed in the table.

So update the complaint to be an error on newer platforms and remove
it completely for older ones that we know are bad (but are not POR for
the Xe driver anyway). Also, re-word the message a little to make it
clearer what the issue is.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Stuart Summers <stuart.summers@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250118005403.2960807-1-John.C.Harrison@Intel.com