usb: chipidea: imx: set over current polarity per dts setting

imx usb over current polarity is low active by default, with
over-current-active-high property added, user can config it to be high
active. Meanwhile keep this setting unchanged for existing platforms
so new platform must set the right value for active low by its usbmisc
init function if over current is enabled.

Signed-off-by: Li Jun <jun.li@nxp.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>