LF-2581-3 ARM: defconfig: add imx_v7_defconfig

Generated for LTS release by:
make ARCH=arm imx_v6_v7_defconfig
make ARCH=arm savedefconfig
cp -avf defconfig arch/arm/configs/imx_v7_defconfig

Plus items below compared with L5.4 release
CONFIG_VMSPLIT_2G=y

And remove:
CONFIG_SOC_IMX5
CONFIG_SOC_VF610
CONFIG_DEBUG_PREEMPT

Based on commit: 547c7f50e3fc (next-nxp-20201028)

Acked-by: Jason Liu <jason.hui.liu@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>