dt-bindings: phy: intel-emmc-phy: Add YAML schema for LGM eMMC PHY

Add a YAML schema to use the host controller driver with the
eMMC PHY on Intel's Lightning Mountain SoC.
Signed-off-by: Ramuthevar Vadivel Murugan <vadivel.muruganx.ramuthevar@linux.intel.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/intel,lgm-emmc-phy.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/phy/intel,lgm-emmc-phy.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Intel Lightning Mountain(LGM) eMMC PHY Device Tree Bindings
+
+maintainers:
+  - Ramuthevar Vadivel Murugan <vadivel.muruganx.ramuthevar@linux.intel.com>
+
+description: |+
+  Bindings for eMMC PHY on Intel's Lightning Mountain SoC, syscon
+  node is used to reference the base address of eMMC phy registers.
+
+  The eMMC PHY node should be the child of a syscon node with the
+  required property:
+
+  - compatible:         Should be one of the following:
+                        "intel,lgm-syscon", "syscon"
+  - reg:
+      maxItems: 1
+
+properties:
+  compatible:
+      const: intel,lgm-emmc-phy
+
+  "#phy-cells":
+    const: 0
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+required:
+  - "#phy-cells"
+  - compatible
+  - reg
+  - clocks
+
+examples:
+  - |
+    sysconf: chiptop@e0200000 {
+      compatible = "intel,lgm-syscon", "syscon";
+      reg = <0xe0200000 0x100>;
+
+      emmc-phy: emmc-phy@a8 {
+        compatible = "intel,lgm-emmc-phy";
+        reg = <0x00a8 0x10>;
+        clocks = <&emmc>;
+        #phy-cells = <0>;
+      };
+    };
+...