drm/i915/tgl: Re-enable RPS

We disabled rps while it appeared to be a contributing factor to system
instablity, as that is now resolved, re-enable RPS and see how we fare.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200123135604.1402572-1-chris@chris-wilson.co.uk