dt-bindings: arm: bcm: Convert Northstar 2 to YAML

Update the Broadcom Northstar 2 SoC binding document for boards/SoCs to
use YAML. Verified with dt_binding_check and dtbs_check.
Acked-by: Scott Branden <scott.branden@broadcom.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Documentation/devicetree/bindings/arm/bcm/brcm,ns2.txt

-Broadcom North Star 2 (NS2) device tree bindings
-------------------------------------------------
-
-Boards with NS2 shall have the following properties:
-
-Required root node property:
-
-NS2 SVK board
-compatible = "brcm,ns2-svk", "brcm,ns2";

Documentation/devicetree/bindings/arm/bcm/brcm,ns2.yaml

+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/arm/bcm/brcm,ns2.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Broadcom North Star 2 (NS2) device tree bindings
+
+maintainers:
+  - Ray Jui <rjui@broadcom.com>
+  - Scott Branden <sbranden@broadcom.com>
+
+properties:
+  $nodename:
+    const: '/'
+  compatible:
+    items:
+      - enum:
+        - brcm,ns2-svk
+        - brcm,ns2-xmc
+      - const: brcm,ns2
+
+...