usb: chipidea: Enable user-space triggered role-switching

The flag provided by the USB role-switch logic allow_userspace_control
allows user-space to trigger a role-switch. Several other USB controller
drivers already enable this feature. Let's switch it on for the chipidea
core now also.

Cc: Peter Chen <Peter.Chen@nxp.com>
Cc: Jun Li <jun.li@nxp.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: linux-usb@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Peter Chen <peter.chen@nxp.com>