PCI: altera: Add Altera PCIe MSI driver

Add Altera PCIe MSI driver.  This soft IP supports a configurable number of
vectors, which is a DTS parameter.

[bhelgaas: Kconfig depend on PCIE_ALTERA, typos, whitespace]
Signed-off-by: Ley Foon Tan <lftan@altera.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Rob Herring <robh@kernel.org>
diff --git a/drivers/pci/host/Kconfig b/drivers/pci/host/Kconfig
index f48e6d0..72d8145 100644
--- a/drivers/pci/host/Kconfig
+++ b/drivers/pci/host/Kconfig
@@ -154,4 +154,12 @@
 	  Say Y here if you want to enable PCIe controller support on Altera
 	  FPGA.
 
+config PCIE_ALTERA_MSI
+	bool "Altera PCIe MSI feature"
+	depends on PCIE_ALTERA && PCI_MSI
+	select PCI_MSI_IRQ_DOMAIN
+	help
+	  Say Y here if you want PCIe MSI support for the Altera FPGA.
+	  This MSI driver supports Altera MSI to GIC controller IP.
+
 endmenu