tools: dumpimage: Simplify arguments

tools: dumpimage: Simplify arguments

The dump image utility has very confusing syntax. If called to list image
contents ("-l") it takes the image name as a positional argument. If the
utility is called to extract something from the image, the image must be
provided via the optional argument "-i" as well as the positional argument
but the value passed in the positional argument will be completely
ignored.

Simplify dumpimage by always providing the image as the first positional
argument. Assume we want to dump something from the image if we do not
provide the "-l" option for now.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>