ARM: socfpga: fix uart DMA binding error

socfpga.dtsi is missing the DMA channels for the uart nodes.
This will produce the following errors:

	of_dma_request_slave_channel: dma-names property of node '/soc/serial0@ffc02000' missing or empty
	ttyS0 - failed to request DMA

Provide the correct DMA channels to fix this.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>