Arm: socfpga: pl330: Add #dma-cells for generic dma binding support

This patch adds #dma-cells property to PL330 DMA controller nodes for
supporting generic dma dt bindings on SOCFPGA platform. #dma-channels
and #dma-requests are not required now but added in advance.

Signed-off-by: Padmavathi Venna <padma.v@samsung.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>