dt-bindings: usb: Add generic "usb-phy" property

dt-bindings: usb: Add generic "usb-phy" property

Even though the Generic PHY framework is the more preferable way of
setting the USB PHY up, there are still many dts-files and DT bindings
which rely on having the legacy "usb-phy" specified to attach particular
USB PHYs to USB cores. Let's have the "usb-phy" property described in
the generic USB HCD binding file so it would be validated against the
nodes in which it's specified. Mark the property as deprecated to
discourage the developers from using it.

Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20201210090944.16283-7-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>