GPL License Exception:

Even though U-Boot in general is covered by the GPL-2.0/GPL-2.0+,
this does *not* cover the so-called "standalone" applications that
use U-Boot services by means of the jump table provided by U-Boot
exactly for this purpose - this is merely considered normal use of
U-Boot, and does *not* fall under the heading of "derived work".

The following files define interfaces to U-Boot:
  * include/image.h
  * include/export.h
  * arch/*/include/asm/u-boot.h
  * examples/standalone/stubs.c

Including these (unmodified) files in another file is considered normal
use of U-Boot, and does *not* fall under the heading of "derived work".
-- Wolfgang Denk