hw/core/split-irq: Device that splits IRQ lines

hw/core/split-irq: Device that splits IRQ lines

In some board or SoC models it is necessary to split a qemu_irq line
so that one input can feed multiple outputs.  We currently have
qemu_irq_split() for this, but that has several deficiencies:
 * it can only handle splitting a line into two
 * it unavoidably leaks memory, so it can't be used
   in a device that can be deleted

Implement a qdev device that encapsulates splitting of IRQs, with a
configurable number of outputs.  (This is in some ways the inverse of
the TYPE_OR_IRQ device.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180220180325.29818-13-peter.maydell@linaro.org