usb: isp1760: use dr_mode binding

There is already a binding to describe the dual role mode (dr_mode),
use that instead of defining a new one (port1-otg).

Update driver code and devicetree files that use that port1-otg
binding.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Link: https://lore.kernel.org/r/20210513084717.2487366-7-rui.silva@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>