ARM: imx_v6_v7_defconfig: Select VF610_ADC

The vf610 adc driver is present on Vybrid, MX6SX, MX6UL and MX7D.

Select it by default.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>