drm/i915: Add RP1 render P state thresholds in CHV

This is useful for userspace utilities to verify and micromanaging
the increase/decrease frequncy.

v2: Use vlv_gpu_freq to get freq (Deepak)

Signed-off-by: Deepak S <deepak.s@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>