drm/i915/skl: Restrict the ring frequency table programming to SKL
drm/i915/skl: Restrict the ring frequency table programming to SKL

Ring frequency table programming is not required on BXT. Added separate
checks to enable the programming only for SKL & skip for BXT.

v2: Removed the BXT check from gen6_update_ring_freq function

Issue: VIZ-5144
Signed-off-by: Akash Goel <43c08a34c75a22c720e674b49d601292087a879d@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
Signed-off-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@ffwll.ch>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs