doc: usb: ci-hdrc-usb2: add property over-current-active-high

Adding over-current-active-high to indicate the over current flag
is high active as typically we use active low for over current
polarity.
Signed-off-by: NLi Jun <jun.li@nxp.com>
Signed-off-by: NPeter Chen <peter.chen@nxp.com>
Acked-by: NRob Herring <robh@kernel.org>

Documentation/devicetree/bindings/usb/ci-hdrc-usb2.txt

@@ -81,6 +81,8 @@ i.mx specific properties
 - fsl,usbmisc: phandler of non-core register device, with one
   argument that indicate usb controller index
 - disable-over-current: disable over current detect
+- over-current-active-high: over current signal polarity is high active,
+  typically over current signal polarity is low active.
 - external-vbus-divider: enables off-chip resistor divider for Vbus
 
 Example: