irqchip/loongarch-avec: Add multi-nodes topology support

avecintc_init() enables the Advanced Interrupt Controller (AVEC) of
the boot CPU node, but nothing enables the AVEC on secondary nodes.

Move the enablement to the CPU hotplug callback so that secondary nodes get
the AVEC enabled too. In theory enabling it once per node would be
sufficient, but redundant enabling does no hurt, so keep the code simple
and do it unconditionally.

Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://lore.kernel.org/all/20250111023704.17285-1-zhangtianyang@loongson.cn