arm64: zynqmp: Add missing #dma-cells property

Requesting the dma controllers fails if #dma-cells is not defined. Add
the missing property.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Link: https://lore.kernel.org/r/20220112151541.1328732-3-m.tretter@pengutronix.de


Signed-off-by: Michal Simek <michal.simek@xilinx.com>