LoongArch: Move irqchip function prototypes to irq-loongson.h

Some irqchip functions are only for internal use by irqchip drivers, so
move their prototypes from asm/irq.h to drivers/irqchip/irq-loongson.h.

All related driver files include the new irq-loongson.h.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240823103936.25092-1-zhangtianyang@loongson.cn