uinput: Implement FreeBSD fetch_syspath_and_devnode()

uinput: Implement FreeBSD fetch_syspath_and_devnode()

Implement a FreeBSD version of fetch_syspath_and_devnode().
FreeBSD does not have sysfs, so instead fetch the device node directly
as as this matches with what is returned by the UI_GET_SYSNAME ioctl().
Since there is no sysfs, libevdev_uinput.syspath will always be set to NULL.

If the ioctl fail, return -1 from fetch_syspath_and_devnode(), since
there is no other way to figure out the device node path.

Signed-off-by: Niclas Zeising <zeising@daemonic.se>