During this board's sync with Linux device trees, it was observed that
it doesn't use the same compatible string for the RTC node as in U-Boot.
This change makes the RTC compatible strings match, for a smoother sync.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Reviewed-by: Michael Walle <michael@walle.cc> Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>