irq: introduce qemu_irq_proxy()

irq: introduce qemu_irq_proxy()

In some cases we have a circular dependency involving irqs - the irq
controller depends on a bus, which in turn depends on the irq controller.
Add qemu_irq_proxy() which acts as a passthrough, except that the target
irq may be set later on.

Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Avi Kivity <[email protected]>
Signed-off-by: Anthony Liguori <[email protected]>