drm/i915: Eliminate Gen9 special case

If we insert blitter forcewake domain entries in the range
table we can eliminate that special case and simplify the
code in a few macros. This will enable more unification later.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>