PCI: xgene-msi: Include <linux/irqdomain.h> explicitly

pci-xgene-msi.c uses irq_domain_add_linear() and related interfaces, so it
needs <linux/irqdomain.h> but doesn't include it directly; it relies on the
fact that <linux/of_irq.h> includes it.

But pci-xgene-msi.c *doesn't* need <linux/of_irq.h> itself.  Include
<linux/irqdomain.h> directly to remove this implicit dependency so a future
patch can drop <linux/of_irq.h>.

Link: https://lore.kernel.org/r/20221031153954.1163623-5-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Author: bjorn-helgaas

drivers/pci/controller/pci-xgene-msi.c

@@ -8,6 +8,7 @@
  */
 #include <linux/cpu.h>
 #include <linux/interrupt.h>
+#include <linux/irqdomain.h>
 #include <linux/module.h>
 #include <linux/msi.h>
 #include <linux/of_irq.h>