irqchip/gic-v3-its: Add support for device tree msi-map and msi-mask

Some platform devices create child devices dynamically and require the
parent device's msi-map to map device IDs to actual sideband information.

A typical use case is using ITS as a PCIe Endpoint Controller(EPC)'s
doorbell function, where PCI hosts send TLP memory writes to the EP
controller. The EP controller converts these writes to AXI transactions
and appends platform-specific sideband information.

EPC's DTS will provide such information by msi-map and msi-mask. A
simplified dts as

pcie-ep@10000000 {
	...
	msi-map = <0 &its 0xc 8>;
                          ^^^ 0xc is implement defined sideband information,
			      which append to AXI write transaction.
	           ^ 0 is function index.

	msi-mask = <0x7>
}

Check msi-map if msi-parent missed to keep compatility with existing systems.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250414-ep-msi-v18-5-f69b49917464@nxp.com

Author: nxpfrankli

drivers/irqchip/irq-gic-v3-its-msi-parent.c

@@ -118,6 +118,14 @@ static int of_pmsi_get_dev_id(struct irq_domain *domain, struct device *dev,
 		index++;
 	} while (!ret);
 
+	if (ret) {
+		struct device_node *np = NULL;
+
+		ret = of_map_id(dev->of_node, dev->id, "msi-map", "msi-map-mask", &np, dev_id);
+		if (np)
+			of_node_put(np);
+	}
+
 	return ret;
 }