commands/*: Replace license and copyright boilerplate by SPDX identfiers ...

While at it also drop references to the non-existing CREDITS file and do
some small rearrangements for some uniform formatting.
(SPDX-License-Identifier first, then copyright texts and then an empty
line.)

The advantage is that these specifiers are machine-parseable which helps
license conformance.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

bootchooser: fix help message ...

The descriptions of -a and -p were mismatched.

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

boot: add framework for redundant boot scenarios ...

There are several use cases where a redundant Linux system is needed. The
barebox bootchooser framework provides the building blocks to model different
use cases without the need to start from the scratch over and over again.

The bootchooser works on abstract boot targets, each with a set of properties
and implements an algorithm which selects the highest priority target to boot.

See the documentation contained in this patch for more information.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>