Documentation: brcmstb-l2: Add Broadcom STB Level-2 interrupt controller binding

This patch adds the Device Tree binding document for the Broadcom
Set-top-box Level 2 interrupt controller hardware.

Signed-off-by: Brian Norris <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Florian Fainelli <[e-mail]>
Signed-off-by: Jason Cooper <[e-mail]>

Documentation/devicetree/bindings/interrupt-controller/brcm,l2-intc.txt

···
+Broadcom Generic Level 2 Interrupt Controller
+
+Required properties:
+
+- compatible: should be "brcm,l2-intc"
+- reg: specifies the base physical address and size of the registers
+- interrupt-controller: identifies the node as an interrupt controller
+- #interrupt-cells: specifies the number of cells needed to encode an
+  interrupt source. Should be 1.
+- interrupt-parent: specifies the phandle to the parent interrupt controller
+  this controller is cacaded from
+- interrupts: specifies the interrupt line in the interrupt-parent irq space
+  to be used for cascading
+
+Optional properties:
+
+- brcm,irq-can-wake: If present, this means the L2 controller can be used as a
+  wakeup source for system suspend/resume.
+
+Example:
+
+hif_intr2_intc: interrupt-controller@f0441000 {
+	compatible = "brcm,l2-intc";
+	reg = <0xf0441000 0x30>;
+	interrupt-controller;
+	#interrupt-cells = <1>;
+	interrupt-parent = <&intc>;
+	interrupts = <0x0 0x20 0x0>;
+};