README: add procedure to retreive meta-openembedded

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
SAMA5D3 Xplained image: remove zImage from UBI

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
kernel: add more modules and network options

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