Add documentation describing the device-tree properties for the Ravelin pinctrl driver. Change-Id: Iedc4f70d5aa8b387d9fbe99753438ba322106b2b Signed-off-by: Yue Liu <quic_yueliu@quicinc.com> Signed-off-by: Swetha Chikkaboraiah <quic_schikk@quicinc.com>