irqchip: Make irqchip_init() usable on pure ACPI systems

Pure ACPI systems (e.g., LoongArch) do not need OF_IRQ, but still
require irqchip_init() to perform the ACPI irqchip probing,
even when OF_IRQ isn't selected.

Relax the dependency to enable the generic irqchip support when
ACPI_GENERIC_GSI is configured.

Signed-off-by: Huacai Chen <[e-mail]>
Tested-by: Tiezhu Yang <[e-mail]>
[maz: revamped commit message]
Signed-off-by: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/irqchip/Kconfig

···
 
 config IRQCHIP
 	def_bool y
-	depends on OF_IRQ
+	depends on (OF_IRQ || ACPI_GENERIC_GSI)
 
 config ARM_GIC
 	bool

include/linux/of_irq.h

···
 extern int of_irq_to_resource(struct device_node *dev, int index,
 			      struct resource *r);
 
-extern void of_irq_init(const struct of_device_id *matches);
-
 #ifdef CONFIG_OF_IRQ
+extern void of_irq_init(const struct of_device_id *matches);
 extern int of_irq_parse_one(struct device_node *device, int index,
 			  struct of_phandle_args *out_irq);
 extern int of_irq_count(struct device_node *dev);
···
 extern void of_msi_configure(struct device *dev, struct device_node *np);
 u32 of_msi_map_id(struct device *dev, struct device_node *msi_np, u32 id_in);
 #else
+static inline void of_irq_init(const struct of_device_id *matches)
+{
+}
 static inline int of_irq_parse_one(struct device_node *device, int index,
 				   struct of_phandle_args *out_irq)
 {