ARM: imx_v6_v7_defconfig: Enable USB GPIO extcon support

Enable USB GPIO extcon support aka CONFIG_EXTCON_USB_GPIO as e.g. used
on Colibri iMX6 and Colibri iMX7 for USB device/host role switching.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>