Add missing license header to layout.c

The file was written by Stefan Reinauer for coresystems GmbH in 2005, as
confirmed on IRC.

Corresponding to flashrom svn r198 and coreboot v2 svn r3126.

Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>
Acked-by: Stefan Reinauer <stepan@coresystems.de>