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>

kbuild: Make scripts executable

The Makefiles call the respective interpreter explicitly, but this makes
it easier to use the scripts manually.

(This commit follows commit 06ed5c2bfaca of Linux Kernel)

Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

Makefile: add a new script to check -fstack-usage support

If -fstack-usage option is given to crosstools
that do not support it, gcc displays a warning message
but still exits with status 0.

This means we can not rely on $(call cc-option,...)
to detect if -fstack-usage option is supported or not.

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