arm64: dts: rockchip: Add nodes for buttons on rk3399-roc-pc

rk3399-roc-pc has a power and a recovery button, enable them.

Signed-off-by: Markus Reichl <m.reichl@fivetechno.de>
Link: https://lore.kernel.org/r/1ce152cc-bd6b-63af-7892-221e084d087f@fivetechno.de


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