drm/i915: Store the requested frequency whilst RPS is disabled

If intel_set_rps() is called whilst the hw is disabled, just store the
requested frequency (from the user) for application when we wake the hw
up.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170220094713.22874-2-chris@chris-wilson.co.uk


Reviewed-by: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com>