arm64: dts: rockchip: add leds node on rk3328-rock64

Add led nodes on Rock64.
Use heartbeat trigger for the red standby led and
use mmc0 trigger for the white power led.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>