Merge branch irq/ipi-mux into irq/irqchip-next

* irq/ipi-mux:
  : .
  : Extract the IPI muxing facility from the Apple AIC driver and
  : move it over to core code. The riscv irqchip code will eventually
  : make use of this.
  : .
  genirq/ipi-mux: Use irq_domain_alloc_irqs()
  irqchip/apple-aic: Move over to core ipi-mux
  genirq: Add mechanism to multiplex a single HW IPI

Signed-off-by: Marc Zyngier <maz@kernel.org>