dt-bindings: Add AXG shared MIPI/PCIE analog PHY bindings

Add documentation for the shared MIPI/PCIE analog PHY found in AXG
SoCs.
Signed-off-by: Remi Pommarel <repk@triplefau.lt>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/phy/amlogic,meson-axg-mipi-pcie-analog.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/phy/amlogic,meson-axg-mipi-pcie-analog.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Amlogic AXG shared MIPI/PCIE analog PHY
+
+maintainers:
+  - Remi Pommarel <repk@triplefau.lt>
+
+properties:
+  compatible:
+    const: amlogic,axg-mipi-pcie-analog-phy
+
+  reg:
+    maxItems: 1
+
+  "#phy-cells":
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - "#phy-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    mpphy: phy@0 {
+          compatible = "amlogic,axg-mipi-pcie-analog-phy";
+          reg = <0x0 0x0 0x0 0xc>;
+          #phy-cells = <1>;
+    };