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>

commands: unify newlines for options ...

The BAREBOX_CMD_HELP_OPT macro adds a newline to the string, but users
of the macro inconsistently add another newline resulting in empty
newlines for some commands, but not for others. Remove any newline in
the description and rely on BAREBOX_CMD_HELP_OPT for the formatting.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

commands: add of_display_timings ...

A lot of boards use display-timings nodes to define the timings of one or more
displays. This command makes it possible to list and select displays which are
defined in a device tree.

Signed-off-by: Teresa Gámez <t.gamez@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>