Download poky-morty. Yocto v2.2. Put "meta-xavier" repository among the other meta.
In the main poky-morty folder :
source oe-init-build-env build/rpi
bitbake rpi-image-timochess
After a couple of hours of downloading/compiling/packaging a full Linux distribution is here : ./tmp/deploy/images/raspberrypi2/rpi-image-timochess-raspberrypi2-*.rootfs.rpi-sdimg
You can use etcher or dd to flash your SD card.