PS/2 mouse and keyboard not disabled when adding USB devices
Description of problem:
Documentation (such as https://www.qemu.org/docs/master/system/qemu-manpage.html or https://www.qemu.org/docs/master/system/devices/usb.html) says that enabling a USB keyboard or mouse (or tablet) will disable the PS/2 equivalent, but it seems both are present instead.
Steps to reproduce:
1. Pass a `-usbdevice` or `-device` option to QEMU.
2. Boot Haiku.
3. Find two identical devices in Preferences > Input, both `Extended PS/2 Mouse 1` and `USB Tablet 1`, as well as `AT Keyboard 1` and `USB Keyboard 1`.
Additional information:
The content of /var/log/syslog, which shows discovery of PS/2 devices: [syslog.zst](/uploads/7ed067538c94edfdbaf35ec92a422c68/syslog.zst)