ARM: imx_v6_v7_defconfig: Enable for DHCOM devices required RTC_DRV_RV3029C2

All imx6 DHCOM devices uses a on module gold cap/battery powered i2c rtc
"microcrystal,rv3029", which isn't enabled in the imx_v6_v7_defconfig.

The rtc for all imx6 DHCOM devices is defined in: imx6qdl-dhcom-som.dtsi
To have a working clock on all imx6qdl DHCOM based devices, enable the driver.

Signed-off-by: Johann Neuhauser <jneuhauser@dh-electronics.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>