irqdomain: Make build work for CONFIG_GENERIC_IRQ_CHIP=n

ld: kernel/irq/irqdomain.o: in function `irq_domain_instantiate':
kernel/irq/irqdomain.c:296:(.text+0x10dd): undefined reference to `irq_domain_alloc_generic_chips'
ld: kernel/irq/irqdomain.c:313:(.text+0x1218): undefined reference to `irq_domain_remove_generic_chips'
ld: kernel/irq/irqdomain.o: in function `irq_domain_remove':
kernel/irq/irqdomain.c:349:(.text+0x1ddf): undefined reference to `irq_domain_remove_generic_chips'

Provide the required stubs.

Fixes: e6f67ce3 ("irqdomain: Add support for generic irq chips creation before publishing a domain")
Reported-by: Borislav Betkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/irq.h

@@ -1182,9 +1182,19 @@ int devm_irq_setup_generic_chip(struct device *dev, struct irq_chip_generic *gc,
 
 struct irq_chip_generic *irq_get_domain_generic_chip(struct irq_domain *d, unsigned int hw_irq);
 
+#ifdef CONFIG_GENERIC_IRQ_CHIP
 int irq_domain_alloc_generic_chips(struct irq_domain *d,
 				   const struct irq_domain_chip_generic_info *info);
 void irq_domain_remove_generic_chips(struct irq_domain *d);
+#else
+static inline int
+irq_domain_alloc_generic_chips(struct irq_domain *d,
+			       const struct irq_domain_chip_generic_info *info)
+{
+	return -EINVAL;
+}
+static inline void irq_domain_remove_generic_chips(struct irq_domain *d) { }
+#endif /* CONFIG_GENERIC_IRQ_CHIP */
 
 int __irq_alloc_domain_generic_chips(struct irq_domain *d, int irqs_per_chip,
 				     int num_ct, const char *name,