irqchip/gicv3: Add a iort_pmsi_get_dev_id() prototype

iort_pmsi_get_dev_id() has a __weak definition in the driver, and
an override in arm64 specific code, but the declaration is conditional
and not always seen when the copy in the driver gets built:

drivers/irqchip/irq-gic-v3-its-platform-msi.c:41:12: error: no previous prototype for 'iort_pmsi_get_dev_id' [-Werror=missing-prototypes]

Move the existing declaration out of the #ifdef block to ensure
it can be seen in all configurations.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230516200516.554663-5-arnd@kernel.org

Author: arndb

include/linux/acpi_iort.h

@@ -26,13 +26,14 @@ int iort_register_domain_token(int trans_id, phys_addr_t base,
 			       struct fwnode_handle *fw_node);
 void iort_deregister_domain_token(int trans_id);
 struct fwnode_handle *iort_find_domain_token(int trans_id);
+int iort_pmsi_get_dev_id(struct device *dev, u32 *dev_id);
+
 #ifdef CONFIG_ACPI_IORT
 void acpi_iort_init(void);
 u32 iort_msi_map_id(struct device *dev, u32 id);
 struct irq_domain *iort_get_device_domain(struct device *dev, u32 id,
 					  enum irq_domain_bus_token bus_token);
 void acpi_configure_pmsi_domain(struct device *dev);
-int iort_pmsi_get_dev_id(struct device *dev, u32 *dev_id);
 void iort_get_rmr_sids(struct fwnode_handle *iommu_fwnode,
 		       struct list_head *head);
 void iort_put_rmr_sids(struct fwnode_handle *iommu_fwnode,