ARM: imx_v6_v7_defconfig: Select CONFIG_NOP_USB_XCEIV by default

In order to get USB functionality on mx5 boards, we need to select
CONFIG_NOP_USB_XCEIV option, so let's enable it by default.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>