drm/i915: Perform static RPS frequency setup before userspace

As these RPS frequency values are part of our userspace interface, they
must be established before that userspace interface is registered.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1468397438-21226-3-git-send-email-chris@chris-wilson.co.uk