pinctrl: mvebu: armada-370: align VDD cpu-pd pin naming with datasheet

For consistency with the datasheet, this commit renames the VDD
function of the MPP4 pin.

While this changes the DT compatibility, it is not considered to be a
problem since this pin is unlikely to be used for anything but
debugging purposes.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>