Add a description of how to implement verified boot using signed FIT images,
and a simple test which verifies operation on sandbox.

The test signs a FIT image and verifies it, then signs a FIT configuration
and verifies it. Then it corrupts the signature to check that this is
detected.

Signed-off-by: Simon Glass <sjg@chromium.org>

It is difficult to automatically test tracing on most architectures, but
with sandbox it is easy enough to do a simple sanity check.

Signed-off-by: Simon Glass <sjg@chromium.org>

When this test fails it is useful to see the output from U-Boot. Add
printing of this information on failure.

Signed-off-by: Simon Glass <sjg@chromium.org>

The image code is fairly complex with various different options. It would
be useful to have comprehensive tests for this.

As a start, create a script which tries out loading a kernel/ramdisk/fdt
from a FIT and checks that the images appear in the right place in memory.

This uses sandbox which now supports bootm and related features.

Signed-off-by: Simon Glass <sjg@chromium.org>

Since run_command() and run_command_list() are important and a little
confusing, add some basic tests to check that the behaviour is correct.

Note: I am not sure that this should be committed, nor where it should go
in the source tree. Comments welcome.

To run the unit tests use the ut_cmd command available in sandbox:

make sandbox_config
make
./u-boot -c ut_cmd

(To test both hush and built-in parsers, you need to manually change
CONFIG_SYS_HUSH_PARSER in include/configs/sandbox.h and build/run again)

Signed-off-by: Simon Glass <sjg@chromium.org>