[U-Boot] [RFC] rules for SPDX-License-Identifier

[Heinrich Schuchardt]

With c398f2df7ca4 ("checkpatch.pl: update from Linux kernel v4.16")
scripts/checkpatch.ps checks if the SPDX license identifier follows the
rules set forth in
https://www.kernel.org/doc/html/latest/process/license-rules.html

If the SPDX license identifier is not in the first line or it does not
use the right comment style we get a warning like

WARNING: Missing or malformed SPDX-License-Identifier tag in line 1
#37: FILE: lib/efi_selftest/efi_selftest_unaligned.c:1:
+/*

Do we want to apply the same rules as the Linux kernel project?

Best regards

Heinrich