Some notes for RPI3 with Ubuntu 16.04.

# config.txt - original
kernel=uboot.bin
device_tree_address=0x02000000

# config.txt (system-boot partition):
kernel=vmlinuz
initramfs initrd.img followkernel

# to system-boot partition
cp /lib/firmware/4.4.0-1065-raspi2/device-tree/bcm2710-rpi-3-b.dtb
cp /lib/firmware/4.4.0-1065-raspi2/device-tree/overlay

sudo add-apt-repository ppa:ubuntu-raspi2/ppa-rpi3
sudo apt-get update
sudo apt-get install flash-kernel u-boot

sudo apt update
# sudo shutdown -r now (in case)
sudo apt upgrade