dt-bindings/gic-v3: Add documentation for MBI support

Add the required properties to support the MBI feature on GICv3.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Rob Herring <robh@kernel.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lkml.kernel.org/r/20180508121438.11301-10-marc.zyngier@arm.com

Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.txt

@@ -57,6 +57,20 @@ Optional
   occupied by the redistributors. Required if more than one such
   region is present.
 
+- msi-controller: Boolean property. Identifies the node as an MSI
+  controller. Only present if the Message Based Interrupt
+  functionnality is being exposed by the HW, and the mbi-ranges
+  property present.
+
+- mbi-ranges: A list of pairs <intid span>, where "intid" is the first
+  SPI of a range that can be used an MBI, and "span" the size of that
+  range. Multiple ranges can be provided. Requires "msi-controller" to
+  be set.
+
+- mbi-alias: Address property. Base address of an alias of the GICD
+  region containing only the {SET,CLR}SPI registers to be used if
+  isolation is required, and if supported by the HW.
+
 Sub-nodes:
 
 PPI affinity can be expressed as a single "ppi-partitions" node,
@@ -99,6 +113,9 @@ Examples:
 		      <0x0 0x2c020000 0 0x2000>;	// GICV
 		interrupts = <1 9 4>;
 
+		msi-controller;
+		mbi-ranges = <256 128>;
+
 		gic-its@2c200000 {
 			compatible = "arm,gic-v3-its";
 			msi-controller;