Merge branch '2023-08-24-enable-more-features-in-qemu-arm' into next

To quote the author:
Now that the driver for the Bochs VGA card emulated by QEMU is no longer
limited to x86 architectures, this series enables it on arm and arm64 virtual
machines to provide a graphical interface. In line with that series this also
enables console buffering and USB keyboard.

Tested with the Debian 12 installer using GRUB EFI:

  $ tools/buildman/buildman -o build/qemu_arm64 --boards=qemu_arm64 -w
  $ cd build/qemu_arm64
  $ curl -L -o debian.img \
      https://cdimage.debian.org/debian-cd/current/arm64/iso-cd/debian-12.0.0-arm64-netinst.iso
  $ qemu-system-aarch64 \
      -machine virt -cpu cortex-a53 -m 4G -smp 4 \
      -bios u-boot.bin \
      -serial stdio -device VGA \
      -nic user,model=virtio-net-pci \
      -device virtio-rng-pci \
      -device qemu-xhci,id=xhci -device usb-kbd -device usb-tablet \
      -drive if=virtio,file=debian.img,format=raw,readonly=on,media=cdrom

And with one using extlinux.conf:

    $ [...]
    $ curl -L -o head.img.gz \
        https://deb.debian.org/debian/dists/bookworm/main/installer-arm64/current/images/netboot/SD-card-images/gtk/firmware.none.img.gz
    $ curl -L -o partition.img.gz \
        https://deb.debian.org/debian/dists/bookworm/main/installer-arm64/current/images/netboot/SD-card-images/gtk/partition.img.gz
    $ zcat head.img.gz partition.img.gz >debian.img
    $ [...]

Both can get to a graphical installer just fine, in addition to U-Boot
video console showing up in a GTK window.