ARM: dts: meson8m2: mxiii-plus: rename the DCDC2 regulator

ARM: dts: meson8m2: mxiii-plus: rename the DCDC2 regulator

The DCDC2 regulator output is actually called "VDD_EE" in various
Meson8b board schematics. This matches with what Amlogic names it in the
most part of their vendor kernel (there are a few places where it's
actually called VDDAO, schematics of EC-100 suggest that the regulator
output is used for both signals).
While here, also give the regulator an alias as it supplies the Mali GPU
so a phandle to it will be required later on.

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