dt-bindings: phy: Add the M31 based eUSB2 PHY bindings

On SM8750, the M31 eUSB2 PHY is being used to support USB2. Add the
binding definition for the PHY driver.

Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Wesley Cheng <[e-mail]>
Signed-off-by: Melody Olvera <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/devicetree/bindings/phy/qcom,m31-eusb2-phy.yaml

···
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/phy/qcom,m31-eusb2-phy.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Qualcomm M31 eUSB2 phy
+
+maintainers:
+  - Wesley Cheng <[e-mail]>
+
+description:
+  M31 based eUSB2 controller, which supports LS/FS/HS usb connectivity
+  on Qualcomm chipsets.  It is paired with a eUSB2 repeater.
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - qcom,sm8750-m31-eusb2-phy
+
+  reg:
+    maxItems: 1
+
+  "#phy-cells":
+    const: 0
+
+  clocks:
+    items:
+      - description: reference clock
+
+  clock-names:
+    items:
+      - const: ref
+
+  resets:
+    maxItems: 1
+
+  phys:
+    maxItems: 1
+    description:
+      Phandle to eUSB2 repeater
+
+  vdd-supply:
+    description:
+      Phandle to 0.88V regulator supply to PHY digital circuit.
+
+  vdda12-supply:
+    description:
+      Phandle to 1.2V regulator supply to PHY refclk pll block.
+
+required:
+  - compatible
+  - reg
+  - "#phy-cells"
+  - clocks
+  - clock-names
+  - resets
+  - vdd-supply
+  - vdda12-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    usb_1_hsphy: phy@88e3000 {
+        compatible = "qcom,sm8750-m31-eusb2-phy";
+        reg = <0x88e3000 0x29c>;
+
+        clocks = <&tcsrcc_usb2_clkref_en>;
+        clock-names = "ref";
+
+        resets = <&gcc_qusb2phy_prim_bcr>;
+
+        #phy-cells = <0>;
+
+        vdd-supply = <&vreg_l2d_0p88>;
+        vdda12-supply = <&vreg_l3g_1p2>;
+    };