ARM: imx_v6_v7_defconfig: Enable CONFIG_IMX_IPUV3_CORE

Since commit 39b9004d

 (gpu: ipu-v3: Move i.MX IPUv3 core driver out of
staging) the ipuv3 core driver is no longer built bey default.

Select CONFIG_IMX_IPUV3_CORE so that the core ipuv3 code can be built again.

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