ubertest: Add blackbox test uber-script

This modifies CB:23025 further to work with upstream as it is now,
without the syntax changes in the patch chain. I also gave it a new
name since this script is, well, uber.

Since flashrom currently only supports reading/writing ROM-sized files
we can't easily determine a targeted region offset and size except
when a layout file is used. Therefore, some extra arithmetic is needed
in the partial write test and the only modes allowed are clobber mode
and layout mode.

A few other changes:
- Update paths and script name
- Remove write-protect testing support
- Use ROM-sized files only, no region-sized files
- Return error if flashmap or ifd mode are used

Documentation is ported from https://goo.gl/3jNoL7

 into a markdown
file and accompanying SVGs. Minor changes were made for clarity and
formatting, and references to write protect testing have been removed
for the time being.

Tested using a Raspberry Pi with a W25Q16

Change-Id: I1af55d5088c54ee33853009797adbd535a506b49
Signed-off-by: David Hendricks <david.hendricks@gmail.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/38788


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>