ARM: imx: Update imx_v6_v7_defconfig for mag3110 support

The i.MX 6UL EVK has support for the MAG3110 Magnetometer sensor, included
in its base board by default.

So add support for this Magnetometer in the imx_v6_v7_defconfig.

Signed-off-by: Marco Franchi <marco.franchi@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>