board/atmel: provide u-boot env for at91sam9x5ek_mmc

Default bootargs have changed in U-Boot for this board. Build U-Boot
environment and add it to the SD card image to update bootargs.

Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
4 files changed