arm64: dts: rockchip: add phandle to timer0 on rk3368

While the kernel doesn't care s0 much right now, bootloaders like
u-boot need to refine the node on their side, so to make life easier
for everyone add the timer0 phandle for timer0.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Link: https://lore.kernel.org/r/20210209103408.2302218-1-heiko@sntech.de


Signed-off-by: Heiko Stuebner <heiko@sntech.de>