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

pcie-altera-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 pcie-altera-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/20221031153954.1163623-2-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>