ARM: vf610: ddrmc: program Dummy DDRBYTE1/2

The Vybrid reference manual VFXXXRM Rev. 0 10/2016 states in chapter
5.2.6.1 DUMMY PADS (DDR/QuadSPI) that those pads need to be programed
for correct operation of DDR. Assume the default DDR pin configuration
which seems to work well on a Colibri VF50.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>