RP Interrupt Up/Down Frequency Limits register (A014) definition
has changed for SKL. Updated the gen6_rps_limits function as per that

v2: Renamed the function to intel_rps_limits (Chris)
Signed-off-by: NAkash Goel <akash.goel@intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>