board: freescale: t208xrdb: enable Power-On Reset for rev D boards

Starting with board revision D, the MISCCSR CPLD register needs to be
configured to enable Power-on Reset for software reset commands.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>