Use of SysBusDevice::init is deprecated. Use Device::realize instead.

Also introduce TypeInfo::instance_init milkymist_uart_init().

Reported-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>