Link property is the correct way to pass a MemoryRegion to a device
for DMA purposes.

Sidenote: as a sysbus device, this remains non-usercreatable
even though we can drop the specific flag here.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Tested-by: NLaurent Vivier <laurent@vivier.eu>