ARM: at91: dt: add device tree file for SAMA5D4 SoC

Add SAMA5D4 SoC DT file.
Signed-off-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: NJosh Wu <josh.wu@atmel.com>
Signed-off-by: NBo Shen <voice.shen@atmel.com>
Signed-off-by: NBoris BREZILLON <boris.brezillon@free-electrons.com>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>