ARM: dts: meson8b: add the PWM_D output pin

The PWM_D output is used for the VDDEE PWM regulator which supplies for
example the Mali GPU on the EC-100 and Odroid-C1 boards. Add the output
pin the VDDEE regulators can be added.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>