ARM: defconfig: drop CONFIG_USB_FSL_USB2

USB_FSL_USB2 is no longer available for Arm platforms and
was replaced by the chipidea driver.

Fixes: a390bef7 ("usb: gadget: fsl_mxc_udc: Remove the driver")
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>