drm/i915: Don't program eLLC IDI hash mask for gen9+

For gen9 onwards, eDRAM is a true memory side cache. So
there is no need to program idi hash mask as it is for eLLC
only.

v2: INTEL_GEN (Chris), s/has/hash (Matthew)

Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>