openbsd: Split openbsd backend into separate openbsd and netbsd backends

Note the new netbsd_usb.c is an unmodified copy of openbsd_usb.c with
s/obsd/netbsd done on it. The reason for this split is that the openbsd
developers have been working on various improvements for their userspace
usb support, and adding support for those means breaking netbsd support,
by giving netbsd its own backend we can add support for the openbsd
improvements without breaking netbsd support.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
6 files changed