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>

test/py: use " for docstrings

Python's coding style docs indicate to use " not ' for docstrings.

test/py has other violations of the coding style docs, since the docs
specify a stranger style than I would expect, but nobody has complained
about those yet:-)

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

test/py: Implement pytest infrastructure

This tool aims to test U-Boot by executing U-Boot shell commands using the
console interface. A single top-level script exists to execute or attach
to the U-Boot console, run the entire script of tests against it, and
summarize the results. Advantages of this approach are:

- Testing is performed in the same way a user or script would interact
with U-Boot; there can be no disconnect.
- There is no need to write or embed test-related code into U-Boot itself.
It is asserted that writing test-related code in Python is simpler and
more flexible that writing it all in C.
- It is reasonably simple to interact with U-Boot in this way.

A few simple tests are provided as examples. Soon, we should convert as
many as possible of the other tests in test/* and test/cmd_ut.c too.

The hook scripts, relay control utilities, and udev rules I use for my
own HW setup are published at https://github.com/swarren/uboot-test-hooks.

See README.md for more details!

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Tested-by: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org> #v3