treewide: remove references to CREDITS ...

The CREDITS file was removed from barebox in 2015 by commit 6570288f2d97
("Remove the CREDITS file"). Remove references to it from several files.

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

lib: add wchar strdup ...

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Add beginning wchar support ...

EFI uses 16 bit character strings. Add beginning support for this.
Since barebox uses 8 bit strings internally we need conversion functions
to convert between 16 bit and 8 bit strings.

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