Enable evdev on DragonFly and FreeBSD

Some BSDs have native evdev (BSD-licensed) implementation with Linux-compatible API. On FreeBSD >= 13.0 evdev is preferred over libusbhid with new HID subsystem (not yet default atm, set hw.usb.usbhid.enable=1 in /boot/loader.conf). For libudev there's a compatibility wrapper. So, let's enable Linux code on those.

I've applied downstream for Veloren and FishFight. On my PS3-style gamepad only analog sticks seem to work. CC @unrelentingtech