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/int_sqrt.c: Fix compiler warning ...

include int_sqrt.h to have the prototype for the function defined in
this file.

Fixes:
lib/int_sqrt.c:25:15: warning: no previous prototype for 'int_sqrt' [-Wmissing-prototypes]

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

video/edid: Move int_sqrt() out ...

Move int_sqrt() out of drivers/video/edid.c so that it is availible to
other parts of Barebox.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>