Bug#883580: debian-installer: arm64: please ship dtb files

[Leif Lindholm <leif.lindholm@linaro.org>]

X-Debbugs-CC: glikely@secretlab.ca

Please don't ship dtb files at all, including the kernel images.

If firmware does not come with hardware description, that is a
shortcoming of the firmware. If a newer kernel cannot be booted with
an existing device tree, then that is a bug and the kernel should be
patched.

By all means, put a tree of verified actually working device trees
somewhere for platforms known to be provided with bad versions from
their manufacturer.