dt-bindings: usb: Add "ulpi/serial/hsic" PHY types

Aside from the UTMI+ there are also ULPI, Serial and HSIC PHY types
that can be specified in the phy_type HCD property. Add them to the
enumeration of the acceptable values.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20201210090944.16283-5-Sergey.Semin@baikalelectronics.ruSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/usb.yaml

@@ -27,11 +27,13 @@ properties:
   phy_type:
     description:
       Tells USB controllers that we want to configure the core to support a
-      UTMI+ PHY with an 8- or 16-bit interface if UTMI+ is selected. In case
-      this isn't passed via DT, USB controllers should default to HW
-      capability.
+      UTMI+ PHY with an 8- or 16-bit interface if UTMI+ is selected, UTMI+ low
+      pin interface if ULPI is specified, Serial core/PHY interconnect if
+      serial is specified and High-Speed Inter-Chip feature if HSIC is
+      selected. In case this isn't passed via DT, USB controllers should
+      default to HW capability.
     $ref: /schemas/types.yaml#/definitions/string
-    enum: [utmi, utmi_wide]
+    enum: [utmi, utmi_wide, ulpi, serial, hsic]
 
   maximum-speed:
     description: