irqchip/loongson-eiointc: Adjust irqchip driver for 32BIT/64BIT

irqchip/loongson-eiointc: Adjust irqchip driver for 32BIT/64BIT

iocsr_read64()/iocsr_write64() are only available on 64BIT LoongArch
platform, so add and use a pair of helpers, i.e. read_isr()/write_isr()
instead to make the driver work on both 32BIT and 64BIT platforms.

This makes eoiintc_enable() a no-op for 32-bit as it is only required on
64-bit systems.

[ tglx: Make the helpers inline and fixup the variable declaration order ]

Co-developed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260113085940.3344837-4-chenhuacai@loongson.cn