dt-bindings: phy: Add imx8 pcie phy driver support

Add dt-binding for the standalone i.MX8 PCIe PHY driver.
Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Tim Harvey <tharvey@gateworks.com>
Tested-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1638432158-4119-3-git-send-email-hongxing.zhu@nxp.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/phy/fsl,imx8-pcie-phy.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/phy/fsl,imx8-pcie-phy.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Freescale i.MX8 SoC series PCIe PHY Device Tree Bindings
+
+maintainers:
+  - Richard Zhu <hongxing.zhu@nxp.com>
+
+properties:
+  "#phy-cells":
+    const: 0
+
+  compatible:
+    enum:
+      - fsl,imx8mm-pcie-phy
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    items:
+      - const: ref
+
+  resets:
+    maxItems: 1
+
+  reset-names:
+    items:
+      - const: pciephy
+
+  fsl,refclk-pad-mode:
+    description: |
+      Specifies the mode of the refclk pad used. It can be UNUSED(PHY
+      refclock is derived from SoC internal source), INPUT(PHY refclock
+      is provided externally via the refclk pad) or OUTPUT(PHY refclock
+      is derived from SoC internal source and provided on the refclk pad).
+      Refer include/dt-bindings/phy/phy-imx8-pcie.h for the constants
+      to be used.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    enum: [ 0, 1, 2 ]
+
+  fsl,tx-deemph-gen1:
+    description: Gen1 De-emphasis value (optional).
+    $ref: /schemas/types.yaml#/definitions/uint32
+    default: 0
+
+  fsl,tx-deemph-gen2:
+    description: Gen2 De-emphasis value (optional).
+    $ref: /schemas/types.yaml#/definitions/uint32
+    default: 0
+
+  fsl,clkreq-unsupported:
+    type: boolean
+    description: A boolean property indicating the CLKREQ# signal is
+      not supported in the board design (optional)
+
+required:
+  - "#phy-cells"
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+  - fsl,refclk-pad-mode
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/imx8mm-clock.h>
+    #include <dt-bindings/phy/phy-imx8-pcie.h>
+    #include <dt-bindings/reset/imx8mq-reset.h>
+
+    pcie_phy: pcie-phy@32f00000 {
+            compatible = "fsl,imx8mm-pcie-phy";
+            reg = <0x32f00000 0x10000>;
+            clocks = <&clk IMX8MM_CLK_PCIE1_PHY>;
+            clock-names = "ref";
+            assigned-clocks = <&clk IMX8MM_CLK_PCIE1_PHY>;
+            assigned-clock-rates = <100000000>;
+            assigned-clock-parents = <&clk IMX8MM_SYS_PLL2_100M>;
+            resets = <&src IMX8MQ_RESET_PCIEPHY>;
+            reset-names = "pciephy";
+            fsl,refclk-pad-mode = <IMX8_PCIE_REFCLK_PAD_INPUT>;
+            #phy-cells = <0>;
+    };
+...