[PATCH 3/6] commands: add of_dump command

[Holger Schurig]

> +               -f <dtb>        work on <dtb> instead of internal devicetree
> +BAREBOX_CMD_HELP_OPT  ("-f <dtb>",  "work on <dtb> instead of internal devicetree\n")

In my command-rework patches I have used "-f FOO" instead of "-f
<foo>". Two reasons:

1. saves 2 bytes
2. less occurences of column align fixup with extra \t needed