ARM: imx_v6_v7_defconfig: extend RN5T618 PMIC family support

There are new drivers for functionality of that family
(RTC and ADC), so enable them, since they are used by
various i.MX6 boards.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>