arm64: dts: rockchip: add rk3399 SPI DMAs

Add spi dma channels as specified by the rk3399 TRM.

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>