dt-bindings: dw-apb-ictl: Update binding to describe use as primary interrupt controller

Add the required updates to describe the use of dw-apb-ictl as a primary
interrupt controller.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[maz: commit message]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200924071754.4509-5-thunder.leizhen@huawei.com

Documentation/devicetree/bindings/interrupt-controller/snps,dw-apb-ictl.txt

@@ -2,7 +2,8 @@ Synopsys DesignWare APB interrupt controller (dw_apb_ictl)
 
 Synopsys DesignWare provides interrupt controller IP for APB known as
 dw_apb_ictl. The IP is used as secondary interrupt controller in some SoCs with
-APB bus, e.g. Marvell Armada 1500.
+APB bus, e.g. Marvell Armada 1500. It can also be used as primary interrupt
+controller in some SoCs, e.g. Hisilicon SD5203.
 
 Required properties:
 - compatible: shall be "snps,dw-apb-ictl"
@@ -10,6 +11,8 @@ Required properties:
   region starting with ENABLE_LOW register
 - interrupt-controller: identifies the node as an interrupt controller
 - #interrupt-cells: number of cells to encode an interrupt-specifier, shall be 1
+
+Additional required property when it's used as secondary interrupt controller:
 - interrupts: interrupt reference to primary interrupt controller
 
 The interrupt sources map to the corresponding bits in the interrupt
@@ -21,6 +24,7 @@ registers, i.e.
 - (optional) fast interrupts start at 64.
 
 Example:
+	/* dw_apb_ictl is used as secondary interrupt controller */
 	aic: interrupt-controller@3000 {
 		compatible = "snps,dw-apb-ictl";
 		reg = <0x3000 0xc00>;
@@ -29,3 +33,11 @@ Example:
 		interrupt-parent = <&gic>;
 		interrupts = <GIC_SPI 3 IRQ_TYPE_LEVEL_HIGH>;
 	};
+
+	/* dw_apb_ictl is used as primary interrupt controller */
+	vic: interrupt-controller@10130000 {
+		compatible = "snps,dw-apb-ictl";
+		reg = <0x10130000 0x1000>;
+		interrupt-controller;
+		#interrupt-cells = <1>;
+	};