drm/i915: Simplify NEEDS_WaRsDisableCoarsePowerGating

It applies to all gen9 and gen10 now, so we can use a single test
against the gen bitmask.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191115122755.830355-1-chris@chris-wilson.co.uk