arm64: dts: rockchip: add dmac nodes for rk3368 SoCs

Add dmac bus and dmac peri dts nodes for peripherals,
such as I2S, SPI, UART and so on.

Signed-off-by: Huibin Hong <huibin.hong@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>