ARM: imx_v6_v7_defconfig: Remove CONFIG_VMSPLIT_2G

ARM: imx_v6_v7_defconfig: Remove CONFIG_VMSPLIT_2G

CONFIG_VMSPLIT_2G was added to mx5_defconfig by commit 06965c39b4c639
("ARM i.MX5: update defconfig") to fix an issue where mx53 was not
detecting the full 1GiB memory range.

However, as explained by Russell King [1] the correct fix is to select
CONFIG_HIGHMEM.

imx_v6_v7_deconfig inherited such option from mx5_defconfig.

As imx_v6_v7_deconfig has CONFIG_HIGHMEM=y, we should no longer
select such non-standard CONFIG_VMSPLIT_2G option.

[1] http://www.spinics.net/lists/arm-kernel/msg137839.html

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>