drm/i915: Use binary search when looking up forcewake domains

Instead of the existing linear seach, now that we have sorted
range tables, we can do a binary search on them for some
potential miniscule performance gain, but more importantly
for elegance and code size. Hopefully the perfomance gain is
sufficient to offset the function calls which were not there
before.

v2: Removed const cast away.

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