...after U-boot rather than overlapping the back-up SPL.

- Mention work-around for r8152
- Rationalise use of $ and $ prefixes for command lines.

We will never need more than 1 MiB. The current image is not even half that
size.

This prints a welcoming message so the kernel does not panic.

The actual DTB is located via extlinux.conf; we no longer need a DTB
in this image.

Linux is now loaded from /boot on the rootfs.

Not used yet.

It really isn't at this point, but this is a step forward.

...instead of vendor-specific firmware around them.

Note that SPL still uses the vendor firmware format, since that is what
the boot ROM wants.

As part thereof, get rid of the gen_image.sh penultimate tool.

Don't want to carry half a gigabyte of sources that are not there
anymore.