At present this implementation is specific to loading the test FDT. We
plan to load others, so create a generic function to handle this.
The path is now limited to 256 characters, to simplify the code.
When there is an empty argv[0] (which should not happen), the function now
just uses the path as is, with no prefix.
Signed-off-by: Simon Glass <sjg@chromium.org>
73c5cb9dac