drm/i915/pvc: Adjust EU per SS according to HAS_ONE_EU_PER_FUSE_BIT()

If we're treating each bit in the EU fuse register as a single EU
instead of a pair of EUs, then that also cuts the number of potential
EUs per subslice in half.

Fixes: 5ac342ef ("drm/i915/pvc: Add SSEU changes")
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/20220610230801.459577-1-matthew.d.roper@intel.com