ARM: dts: at91: sam9x60: Add DMA bindings for the flexcom nodes

Add dma bindings for flexcom nodes in the soc dtsi file. Users those who
don't wish to use the DMA function for their flexcom functions can
overwrite the dma bindings in the board device tree file.

Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
[durai.manickamkr@microchip.com: fixed code indentation and updated commit log]
Signed-off-by: Durai Manickam KR <durai.manickamkr@microchip.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20230207110651.197268-6-durai.manickamkr@microchip.com