Linux PV on HVM guests can use vkbd, so add a vkbd frontend/backend
pair for HVM guests by default. It is useful because it doesn't
require frequent qemu wakeups as the usb keyboard/mouse does.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>