openrisc_sim_net_init() attempts to connect the IRQ line from the
ethernet device to both CPUs in an SMP configuration by simply caling
sysbus_connect_irq() for it twice.  This doesn't work, because the
second connection simply overrides the first.

Fix this by creating a TYPE_SPLIT_IRQ to split the IRQ in the SMP
case.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Stafford Horne <shorne@gmail.com>
Message-id: 20201127225127.14770-2-peter.maydell@linaro.org