dt-bindings: usb: Add Intel Keem Bay USB controller bindings

Binding description for Intel Keem Bay USB controller.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@intel.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>