q35: Improve sample configuration files

q35: Improve sample configuration files

Instead of having a single sample configuration file,
we now have several:

  * q35-emulated.cfg documents the default devices QEMU
    adds to a q35 guest and the additional devices that
    are pretty much guaranteed to be present in a
    physical q35-based machine;

  * q35-virtio-graphical.cfg can be used to start a
    fully-featured (USB, graphical console, audio, etc.)
    guest that uses VirtIO instead of emulated devices;

  * q35-virtio-serial.cfg is similar but has a minimal
    set of devices and uses the serial console.

All configuration files are fully commented and neatly
organized.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Message-id: 1487326479-8664-2-git-send-email-abologna@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>