hw/arm/virt: add dynamic sysbus device support

hw/arm/virt: add dynamic sysbus device support

Allows sysbus devices to be instantiated from command line by
using -device option. Machvirt creates a platform bus at init.
The dynamic sysbus devices are attached to this platform bus device.

The platform bus device registers a machine init done notifier
whose role will be to bind the dynamic sysbus devices. Indeed
dynamic sysbus devices are created after machine init.

machvirt also registers a notifier that will build the device
tree nodes for the platform bus and its children dynamic sysbus
devices.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 1433244554-12898-4-git-send-email-eric.auger@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>