ARM: dts: rockchip: support highspeed sd-cards for rk3188-radxarock

Add cap-sd-highspeed and cap-mmc-highspeed for rk3188-radxarock
board to make sd cards running faster.
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3188-radxarock.dts

@@ -289,6 +289,8 @@ &mmc0 {
 	vmmc-supply = <&vcc_sd0>;
 
 	bus-width = <4>;
+	cap-mmc-highspeed;
+	cap-sd-highspeed;
 	disable-wp;
 };