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>