Add a new board named after sama5d4_xplained located at board/sama5d4_xplained

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
sama5d3_xplained: fix typo

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
sama5d4_xplained/trivial: fix .dtb name

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>