usbconfig: implement a -v option

Implement a -v option to usbconfig(8), as a shortcut for the most
frequently needed commands dump_device_desc, dump_curr_config_desc,
and show_ifdrv.

While here, implement a real -h option that has been promised by the
man page.

Use <sysexits.h> to declare the utility return codes.

Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D33586
MFC after: 2 weeks