The -sources and -sinks options were defined with OPT_FUNC_ARG flag,
which requires an argument. This caused "Missing argument for option
'sources'" error when running ffprobe -sources without arguments.
Removing OPT_FUNC_ARG flag allows these options to work without
arguments, listing all available devices, while still supporting
optional device name argument for filtering specific devices.
Add "license" as a long-form command line option alongside the existing
"L" short option for showing license information. This maintains
consistent option naming patterns with other commands that provide both
short and long forms (help/?/help, etc.) and improves command line
usability by providing more descriptive option names.
So they don't clutter the standard help output.
-loglevel is marked because there is no need to show two options (-v and
-loglevel) that do the same thing.
