dt-bindings: arm: Add missing LGE SoC platforms

LGE LG131x SoCs have been in use for some time, but the root compatibles
have not been documented. Add them.

Acked-by: Chanho Min <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rob Herring (Arm) <[e-mail]>

Documentation/devicetree/bindings/arm/lge.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/arm/lge.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: LG Electronics SoC Platforms
+
+maintainers:
+  - Chanho Min <[e-mail]>
+
+properties:
+  $nodename:
+    const: "/"
+  compatible:
+    oneOf:
+      - description: Boards with LG1312 Soc
+        items:
+          - const: lge,lg1312-ref
+          - const: lge,lg1312
+
+      - description: Boards with LG1313 SoC
+        items:
+          - const: lge,lg1313-ref
+          - const: lge,lg1313
+
+additionalProperties: true
+...