[U-Boot] SPDX header on .h files

[Fabio Estevam]

On Sun, May 20, 2018 at 8:15 PM, Duncan Hare <dh at synoia.com> wrote:
> What's the correct format for this header?
> Patman is complaining about the SPDX header.

Please check:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/license-rules.rst?h=v4.17-rc6

For header files:

/* SPDX-License-Identifier: <SPDX License Expression> */