ARM: imx_v6_v7_defconfig: Select CONFIG_DRM_I2C_NXP_TDA998X

Select CONFIG_DRM_I2C_NXP_TDA998X so that HDMI output can work by
default on a imx6sx-udoo-neo board.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>