ARM: imx_v6_v7_defconfig: Cleanup imx_v6_v7_defconfig

Generate imx_v6_v7_defconfig by doing:

make savedefconfig

cp defconfig arch/arm/configs/imx_v6_v7_defconfig

No functional change. The goal here is to cleanup imx_v6_v7_defconfig file to
make easier and cleaner the addition of new entries.

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