at91sam9: add defconfig to build an at91sam9 rootfs

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
sama5d3: update defconfig for EK board (non demo rootfs)

Update defconfig file for the sama5d3ek and setup ubi conf.

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