drm: rcar-du: crtc: Register GAMMA_LUT properties

Enable the GAMMA_LUT KMS property using the framework helpers to
register the property and set the associated gamma table maximum size.

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

drivers/gpu/drm/rcar-du/rcar_du_crtc.c

@@ -1136,6 +1136,7 @@ static const struct drm_crtc_funcs crtc_funcs_gen3 = {
 	.set_crc_source = rcar_du_crtc_set_crc_source,
 	.verify_crc_source = rcar_du_crtc_verify_crc_source,
 	.get_crc_sources = rcar_du_crtc_get_crc_sources,
+	.gamma_set = drm_atomic_helper_legacy_gamma_set,
 };
 
 /* -----------------------------------------------------------------------------
@@ -1259,6 +1260,9 @@ int rcar_du_crtc_create(struct rcar_du_group *rgrp, unsigned int swindex,
 	if (rcdu->cmms[swindex]) {
 		rcrtc->cmm = rcdu->cmms[swindex];
 		rgrp->cmms_mask |= BIT(hwindex % 2);
+
+		drm_mode_crtc_set_gamma_size(crtc, CM2_LUT_SIZE);
+		drm_crtc_enable_color_mgmt(crtc, 0, false, CM2_LUT_SIZE);
 	}
 
 	drm_crtc_helper_add(crtc, &crtc_helper_funcs);