ARM: dts: meson8m2: mxiii-plus: add the supply for the Mali GPU

The Mali GPU is supplied by VDD_EE which is provided by the DCDC2
regulator.

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