irqchip/loongson-eiointc: Set CPU affinity only on SMP machines for LoongArch

According to the code comment of "struct irq_chip", the member
"irq_set_affinity" is to set the CPU affinity on SMP machines, so define
and call eiointc_set_irq_affinity() only under CONFIG_SMP.
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240326121130.16622-4-yangtiezhu@loongson.cn

drivers/irqchip/irq-loongson-eiointc.c

@@ -59,6 +59,7 @@ static int cpu_to_eio_node(int cpu)
 	return cpu_logical_map(cpu) / CORES_PER_EIO_NODE;
 }
 
+#ifdef CONFIG_SMP
 static void eiointc_set_irq_route(int pos, unsigned int cpu, unsigned int mnode, nodemask_t *node_map)
 {
 	int i, node, cpu_node, route_node;
@@ -126,6 +127,7 @@ static int eiointc_set_irq_affinity(struct irq_data *d, const struct cpumask *af
 
 	return IRQ_SET_MASK_OK;
 }
+#endif
 
 static int eiointc_index(int node)
 {
@@ -238,7 +240,9 @@ static struct irq_chip eiointc_irq_chip = {
 	.irq_ack		= eiointc_ack_irq,
 	.irq_mask		= eiointc_mask_irq,
 	.irq_unmask		= eiointc_unmask_irq,
+#ifdef CONFIG_SMP
 	.irq_set_affinity	= eiointc_set_irq_affinity,
+#endif
 };
 
 static int eiointc_domain_alloc(struct irq_domain *domain, unsigned int virq,