drm/i915/gt: Plug IPS into intel_rps_set

The old IPS interface did not match the RPS interface that we tried to
plug it into (bool vs int return). Once repaired, our minimal
selftesting is finally happy!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201121190352.15996-1-chris@chris-wilson.co.uk