USB integration on FreeBSD

[clepple]

(Theoretically, this applies to NetBSD and OpenBSD as well, but FreeBSD's USB stack seems more complete at the moment.)

Some code: https://github.com/clepple/nut/tree/devd-usb

Things to do:

• Generate devd.conf files for known USB devices
• Install devd.conf files in the right place (includes detection of *BSD)
• Document the installation process (restarting devd, other permissions issues like scanning the bus, etc.)
• Coordinate with ports maintainer

[clepple]

devd.conf files are installed as of 7460623, and preliminary documentation is in scripts/devd/README

[clepple]

We don't really have a good spot in the manual for OS-specific information, so if we want to close this issue and reopen another documentation-only one, I don't want to hold up the release.

Also, the FreeBSD ports tree can add patches if needed.

[aquette]

Let's reschedule for 2.8.0, so that we can work out the documentation-on-OS-specific-information issue

[clepple]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=191777