drm/i915: only apply GAMMA_MODE IPS WA on HSW

The WA is mentioned in HSW's GAMMA_MODE register documentation, but
not on on BDW's documentation, so let's assume it is not needed there.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -3496,7 +3496,7 @@ static void intel_crtc_load_lut(struct drm_crtc *crtc)
 	/* Workaround : Do not read or write the pipe palette/gamma data while
 	 * GAMMA_MODE is configured for split gamma and IPS_CTL has IPS enabled.
 	 */
-	if (intel_crtc->config.ips_enabled &&
+	if (IS_HASWELL(dev) && intel_crtc->config.ips_enabled &&
 	    ((I915_READ(GAMMA_MODE(pipe)) & GAMMA_MODE_MODE_MASK) ==
 	     GAMMA_MODE_MODE_SPLIT)) {
 		hsw_disable_ips(intel_crtc);