SPDX: Convert all of our single license tags to Linux Kernel style

When U-Boot started using SPDX tags we were among the early adopters and
there weren't a lot of other examples to borrow from. So we picked the
area of the file that usually had a full license text and replaced it
with an appropriate SPDX-License-Identifier: entry. Since then, the
Linux Kernel has adopted SPDX tags and they place it as the very first
line in a file (except where shebangs are used, then it's second line)
and with slightly different comment styles than us.

In part due to community overlap, in part due to better tag visibility
and in part for other minor reasons, switch over to that style.

This commit changes all instances where we have a single declared
license in the tag as both the before and after are identical in tag
contents. There's also a few places where I found we did not have a tag
and have introduced one.

Signed-off-by: Tom Rini <trini@konsulko.com>

scripts: add scripts/show-gnu-make to get GNU Make command name

U-Boot is expected to be built on various platforms.

We should keep in mind that the command 'make' is not always GNU Make,
while all the makefiles are written for GNU Make.

For example, on Linux, people generally do:

make <board>_config; make

But FreeBSD folks do

gmake <board>_config; gmake

(The command 'make' on FreeBSD is BSD Make, not GNU Make)

It is not a good idea to hard-code the command name 'make'
in MAKEALL or buildman.

They should call this helper script and get the command name
for GNU Make.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>