ARM: imx_v6_v7_defconfig: Make usbnet drivers builtin for boot

ARM: imx_v6_v7_defconfig: Make usbnet drivers builtin for boot

Chips such as imx6sll and imx7ulp have no ethernet support so the common
development usecase of nfs boot is supported via usb ethernet dongles.

Add drivers for additional usbnet device directly into the kernel image
produced by the imx defconfig.

This list is based on the usbnet devices supported by uboot.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>