drm/i915: Only use update_wm_{pre,post} for pre-ilk platforms

Now that vlv/chv have more proper wm programming support, let's reduce
the the update_wm_{pre,post} flags to only cover the pre-ilk platforms.
When we finally convert those as well we can drop these flags entirely.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170302171508.1666-12-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -10845,22 +10845,26 @@ int intel_plane_atomic_calc_changes(struct drm_crtc_state *crtc_state,
 			 turn_off, turn_on, mode_changed);
 
 	if (turn_on) {
+		if (INTEL_GEN(dev_priv) < 5)
 			pipe_config->update_wm_pre = true;
 
 		/* must disable cxsr around plane enable/disable */
 		if (plane->id != PLANE_CURSOR)
 			pipe_config->disable_cxsr = true;
 	} else if (turn_off) {
+		if (INTEL_GEN(dev_priv) < 5)
 			pipe_config->update_wm_post = true;
 
 		/* must disable cxsr around plane enable/disable */
 		if (plane->id != PLANE_CURSOR)
 			pipe_config->disable_cxsr = true;
 	} else if (intel_wm_need_update(&plane->base, plane_state)) {
+		if (INTEL_GEN(dev_priv) < 5) {
 			/* FIXME bollocks */
 			pipe_config->update_wm_pre = true;
 			pipe_config->update_wm_post = true;
 		}
+	}
 
 	if (visible || was_visible)
 		pipe_config->fb_bits |= plane->frontbuffer_bit;