drm/i915: Bump CHV PFI credits to 63 when cdclk>=czclk

Switch from using 31 PFI credits to 63 PFI credits when cdclk>=czclk on
CHV. The spec lists both 31 and 63 as "suggested" values, but based on
feedback from hardware folks we should actually be using 63. Originally
I picked the 31 basically by flipping a coin.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NClint Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -6055,7 +6055,7 @@ static void vlv_program_pfi_credits(struct drm_i915_private *dev_priv)
 	if (DIV_ROUND_CLOSEST(dev_priv->cdclk_freq, 1000) >= dev_priv->rps.cz_freq) {
 		/* CHV suggested value is 31 or 63 */
 		if (IS_CHERRYVIEW(dev_priv))
-			credits = PFI_CREDIT_31;
+			credits = PFI_CREDIT_63;
 		else
 			credits = PFI_CREDIT(15);
 	} else {