dts/bindings/usb: Add phys property to STM32 USB yaml

Add phys property, which specifies USB PHY provider,
to STM32 USB yaml files.

Signed-off-by: Yannis Damigos <giannis.damigos@gmail.com>
diff --git a/dts/bindings/usb/st,stm32-otgfs.yaml b/dts/bindings/usb/st,stm32-otgfs.yaml
index 70d79fc..ca2b076 100644
--- a/dts/bindings/usb/st,stm32-otgfs.yaml
+++ b/dts/bindings/usb/st,stm32-otgfs.yaml
@@ -41,4 +41,10 @@
       description: Size of USB dedicated RAM. STM32 SOC's reference
                    manual defines a shared FIFO size.
       generation: define
+
+    phys:
+      type: array
+      category: optional
+      generation: define
+      description: PHY provider specifier
 ...
diff --git a/dts/bindings/usb/st,stm32-otghs.yaml b/dts/bindings/usb/st,stm32-otghs.yaml
index 98c5677..cc387f7 100644
--- a/dts/bindings/usb/st,stm32-otghs.yaml
+++ b/dts/bindings/usb/st,stm32-otghs.yaml
@@ -41,4 +41,10 @@
       description: Size of USB dedicated RAM. STM32 SOC's reference
                    manual defines a shared FIFO size.
       generation: define
+
+    phys:
+      type: array
+      category: optional
+      generation: define
+      description: PHY provider specifier
 ...
diff --git a/dts/bindings/usb/st,stm32-usb.yaml b/dts/bindings/usb/st,stm32-usb.yaml
index cba616c..140e55e 100644
--- a/dts/bindings/usb/st,stm32-usb.yaml
+++ b/dts/bindings/usb/st,stm32-usb.yaml
@@ -48,4 +48,10 @@
       description: Some boards use a USB DISCONNECT pin to enable
                    the pull-up resistor on USB Data Positive signal.
       generation: define, use-prop-name
+
+    phys:
+      type: array
+      category: optional
+      generation: define
+      description: PHY provider specifier
 ...