dt-bindings: usb: add bindings for microchip mpfs musb

Add device tree bindings for the usb controller on
the Microchip PolarFire SoC.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20220117110755.3433142-8-conor.dooley@microchip.com


Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>