Doc: usb: chipidea: need to build both kernel Image and modules

When tried to enable OTG FSM, we need to rebuild both kernel Image
and modules, since there are some codes at gadget modules which are
controlled by related configurations.
Signed-off-by: NPeter Chen <peter.chen@freescale.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/usb/chipidea.txt

@@ -5,7 +5,7 @@ with 2 Freescale i.MX6Q sabre SD boards.
 
 1.1 How to enable OTG FSM in menuconfig
 ---------------------------------------
-Select CONFIG_USB_OTG_FSM.
+Select CONFIG_USB_OTG_FSM, rebuild kernel Image and modules.
 If you want to check some internal variables for otg fsm,
 select CONFIG_USB_CHIPIDEA_DEBUG, there are 2 files which
 can show otg fsm variables and some controller registers value: