doc: usb: ci-hdrc-usb2: Add pinctrl properties definition

Some hardware implementations require to configure pins differently
according to the USB role (host/device), this can be an update of the
pins routing or a simple GPIO value change.

This patch introduces new optional "host" and "device" pinctrls.
If these pinctrls are defined by the device, they are respectively
selected on host/device role start.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Peter Chen <peter.chen@nxp.com>