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: nand-bitflip: Add documentation for option '-c' ...

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

mtd: when creating bitflips the offset has to be page aligned ...

mtd_peb_create_bitflips() assumes the offset is page aligned. Enforce
this and in the nand_bitlfip command print a warning if it's not
aligned.

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

commands: Create nand_bitflip command ...

This adds a command to flip bits in a Nand flash. This is useful for
testing purposes to check if flipped bits are corrected and if the
driver returns the correct number of bitflips.

The command writes a configurable number of bitflips to a single Nand
page. If the -r option is not given the results are reproducible, so
calling the same command twice will revert the bitflips.

The command uses the raw read/write Nand operations which are probably
less tested than the regular read/write operations, so the command may
produce surprising results.

As of writing the command has been tested with the GPMI Nand driver and
the imx-nand driver with fixes posted.

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