PCI: mvebu: add support for MSI

This commit adds support for Message Signaled Interrupts in the
Marvell PCIe host controller. The work is very simple: it simply gets
a reference to the msi_chip associated to the PCIe controller thanks
to the msi-parent DT property, and stores this reference in the
pci_bus structure. This is enough to let the Linux PCI core use the
functions of msi_chip to setup and teardown MSIs.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Thierry Reding <thierry.reding@gmail.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>

Documentation/devicetree/bindings/pci/mvebu-pci.txt

@@ -14,6 +14,8 @@ Mandatory properties:
 - ranges: ranges describing the MMIO registers to control the PCIe
   interfaces, and ranges describing the MBus windows needed to access
   the memory and I/O regions of each PCIe interface.
+- msi-parent: Link to the hardware entity that serves as the Message
+  Signaled Interrupt controller for this PCI controller.
 
 The ranges describing the MMIO registers have the following layout:
 
@@ -86,6 +88,7 @@ pcie-controller {
 	#size-cells = <2>;
 
 	bus-range = <0x00 0xff>;
+	msi-parent = <&mpic>;
 
 	ranges =
 	       <0x82000000 0 0x40000 MBUS_ID(0xf0, 0x01) 0x40000 0 0x00002000	/* Port 0.0 registers */