drm/i915/sseu: Simplify gen11+ SSEU handling

Although gen11 and gen12 architectures supported the concept of multiple
slices, in practice all the platforms that were actually designed only
had a single slice (i.e., note the parameters to 'intel_sseu_set_info'
that we pass for each platform).  We can simplify the code slightly by
dropping the multi-slice logic from gen11+ platforms.

v2:
 - Promote drm_dbg to drm_WARN_ON if the slice fuse register reports
   unexpected fusing.  (Tvrtko)

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220601150725.521468-4-matthew.d.roper@intel.com