irqchip/loongson-pch-lpc: Enable building on MIPS Loongson64

irqchip/loongson-pch-lpc: Enable building on MIPS Loongson64

As the driver now supports OF-based platforms, it's now possible to use it
on MIPS Loongson64 machines.

Drop the requirement of LOONGARCH for this driver, to allow build on
both MIPS-based and LoongArch-based Loongson systems.

Signed-off-by: Icenowy Zheng <zhengxingda@iscas.ac.cn>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://patch.msgid.link/20260321092032.3502701-7-zhengxingda@iscas.ac.cn