drm/i915: Update prop, int co-eff and gain threshold for CHV

drm/i915: Update prop, int co-eff and gain threshold for CHV

This patch implements latest PHY changes in Gain, prop and int co-efficients
based on the vco freq.

v2: Split the original changes into multiple smaller patches based on
review by Ville

v3: Addressed Ville's review comments. Fixed the error introduced in v2.
Clear the old bits before we modify those bits as part of RMW.

v4: TDC target cnt is 10 bits and not 8 bits (Ville)

Signed-off-by: Vijay Purushothaman <vijay.a.purushothaman@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>