drm/i915: Change CHV SKU400 GPU freq divider to 10

According to "Cherryview_GFXclocks_y14w36d1.xlsx" the GPU frequency
divider should be 10 in when the CZ clock is 400 MHz. Change the code
to agree so that we report the correct frequencies.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Deepak <S&lt;deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>