irqchip/loongarch-avec: Adjust irqchip driver for 32BIT/64BIT

irqchip/loongarch-avec: Adjust irqchip driver for 32BIT/64BIT

csr_read64() is only available on 64BIT LoongArch platform, so use the
recently added adaptive csr_read() instead to make the driver work on both
32BIT and 64BIT platforms.

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

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/20260113085940.3344837-2-chenhuacai@loongson.cn