1. add buildroot to the build targets (still not used as rootfs).
2. bootstrap ubuntu 19.04 rootfs using multistrap and
qemu-aarch64-static
3. build and install restool under ubuntu rootfs
4. Image and dtb are added to ubuntu 19.04 partition
5. The micro SD now contains a file called ubuntu-core.img. That image
can be copied to NVME drive, SATA drive or USB drive and using it's
PARTUUID the kernel finds the right root partition and mounts it.

To install the image on NVME M.2 drive; stop u-boot count down and run -

load mmc 0:1 0xa4000000 ubuntu-core.img
nvme scan
nvme write 0xa4000000 0 262144
nvme write 0xac000000 262144 262144
nvme write 0xb4000000 524288 204800

To install to SATA drive -
load mmc 0:1 0xa4000000 ubuntu-core.img
scsi reset
scsi write 0xa4000000 0 0xb2000

then run 'boot'.

First thing after booting ubuntu -
1. resize the main partition to include bigger partition than the default.
2. run resize2fs /dev/nvme0n1p1 or resize2fs /dev/sda1 to enlarge the
rootfs to new partition
3. run 'dhclient'
4. get ntp clock by running 'ntpdate pool.ntp.org'
5. store clock to RTC chip 'hwclock -w'
Signed-off-by: Rabeeh Khoury <rabeeh@solid-run.com>