irqchip/ingenic: Get rid of the legacy IRQ domain

Get rid of the legacy IRQ domain and hardcoded IRQ base, since all the
Ingenic drivers and platform code have been updated to use devicetree.

This also fixes the kernel being flooded with messages like:

 irq: interrupt-controller@10001000 didn't like hwirq-0x0 to VIRQ8 mapping (rc=-19)

Fixes: 8bc7464b

 ("irqchip: ingenic: Alloc generic chips from IRQ domain").
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: H. Nikolaus Schaller <hns@goldelico.com>
Tested-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200113163329.34282-2-paul@crapouillou.net