Add atmel-ssc for device tree support

Match "atmel,at91rm9200-ssc" for using pdc for data transfer
Match "atmel,at91sam9g45-ssc" for using dma for data transfer
Signed-off-by: NBo Shen <voice.shen@atmel.com>
Acked-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>