ARM: dts: rockchip: Add SPI DMA into rk3288.dtsi

Now that SPI DMA has been fixed on rk3288 we can enable it.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Alexandru M Stan <amstan@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>