Several tests are intending to test some serial/console related
bits but aren't setting QEMU_CAPS_CHARDEV. This will soon be enabled
unconditionally so let's add it ahead of time.

* q35-virt-manager-basic: Intended to test a virt-manager q35 config,
    which will include a serial/console device
* console-compat*: console/serial XML compat handling
* bios: Needs a serial device for sgabios CLI
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Signed-off-by: NCole Robinson <crobinso@redhat.com>