drm/i915: Report requested frequency alongside current frequency in debugfs

It can be useful to compare at times the current vs requested frequency
of the GPU, so provide the contents of RPNSWREQ alonside CAGF.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>