To get stable CRCs from the DP CRC source we need to reset the
scrambler for each frame. Enable the reset feature when grabbing
CRCs for pipe C on CHV. Pipes A and B were already covered due
sharing the code with VLV.

We can safely extend PIPE_SCRAMBLE_RESET_MASK to deal with CHV since
the extra bit was MBZ on the older platforms.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>