Add the device tree file for sama5d3 Xplained board.
The dts files are copied from the Linux-4.9, do changes as below.
- add the "u-boot,dm-pre-reloc" property to determine which nodes
which are needed by SPL and by the board_init_f stage.
- fix the compile warning.
Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
