dt-bindings: firmware: convert meson_sm.txt to dt-schema

Convert the Amlogic Secure Monitor bindings to dt-schema.

Take in account usage the used variant with amlogic,meson-gx-sm.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221117-b4-amlogic-bindings-convert-v2-1-36ad050bb625@linaro.orgSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>

Documentation/devicetree/bindings/firmware/amlogic,meson-gxbb-sm.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/firmware/amlogic,meson-gxbb-sm.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Amlogic Secure Monitor (SM)
+
+description:
+  In the Amlogic SoCs the Secure Monitor code is used to provide access to the
+  NVMEM, enable JTAG, set USB boot, etc...
+
+maintainers:
+  - Neil Armstrong <neil.armstrong@linaro.org>
+
+properties:
+  compatible:
+    oneOf:
+      - const: amlogic,meson-gxbb-sm
+      - items:
+          - const: amlogic,meson-gx-sm
+          - const: amlogic,meson-gxbb-sm
+
+  power-controller:
+    type: object
+    $ref: /schemas/power/amlogic,meson-sec-pwrc.yaml#
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    firmware {
+        secure-monitor {
+            compatible = "amlogic,meson-gxbb-sm";
+        };
+    };

Documentation/devicetree/bindings/firmware/meson/meson_sm.txt

-* Amlogic Secure Monitor
-
-In the Amlogic SoCs the Secure Monitor code is used to provide access to the
-NVMEM, enable JTAG, set USB boot, etc...
-
-Required properties for the secure monitor node:
-- compatible: Should be "amlogic,meson-gxbb-sm"
-
-Example:
-
-	firmware {
-		sm: secure-monitor {
-			compatible = "amlogic,meson-gxbb-sm";
-		};
-	};