irqchip/apple-aic: Move over to core ipi-mux

Now that the complexity of the AIC IPI mux has been copied into
the core code for the benefit of the riscv architecture,
shrink the AIC driver by the same amount by using that infrastructure.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Acked-by: Hector Martin <marcan@marcan.st>
Link: https://lore.kernel.org/r/20230103141221.772261-10-apatel@ventanamicro.com