dt-bindings: nvmem: Convert snvs lpgpr to json-schema

Convert the snvs lpgpr binding to DT schema format using json-schema.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Link: https://lore.kernel.org/r/1596610172-30323-1-git-send-email-Anson.Huang@nxp.comSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/nvmem/snvs-lpgpr.txt

-Device tree bindings for Low Power General Purpose Register found in i.MX6Q/D
-and i.MX7 Secure Non-Volatile Storage.
-
-This DT node should be represented as a sub-node of a "syscon",
-"simple-mfd" node.
-
-Required properties:
-- compatible: should be one of the fallowing variants:
-	"fsl,imx6q-snvs-lpgpr" for Freescale i.MX6Q/D/DL/S
-	"fsl,imx6ul-snvs-lpgpr" for Freescale i.MX6UL
-	"fsl,imx7d-snvs-lpgpr" for Freescale i.MX7D/S
-
-Example:
-snvs: snvs@020cc000 {
-	compatible = "fsl,sec-v4.0-mon", "syscon", "simple-mfd";
-	reg = <0x020cc000 0x4000>;
-
-	snvs_lpgpr: snvs-lpgpr {
-		compatible = "fsl,imx6q-snvs-lpgpr";
-	};
-};

Documentation/devicetree/bindings/nvmem/snvs-lpgpr.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/nvmem/snvs-lpgpr.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Low Power General Purpose Register found in i.MX Secure Non-Volatile Storage
+
+maintainers:
+  - Oleksij Rempel <o.rempel@pengutronix.de>
+
+properties:
+  compatible:
+    enum:
+      - fsl,imx6q-snvs-lpgpr
+      - fsl,imx6ul-snvs-lpgpr
+      - fsl,imx7d-snvs-lpgpr
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    snvs@20cc000 {
+        compatible = "fsl,sec-v4.0-mon", "syscon", "simple-mfd";
+        reg = <0x20cc000 0x4000>;
+
+        snvs_lpgpr: snvs-lpgpr {
+            compatible = "fsl,imx6q-snvs-lpgpr";
+        };
+    };