ARM: sun8i: sina33: add cpu-supply

This adds the cpu-supply DT property to the cpu0 DT node needed by
the board to adapt the regulator voltage depending on the currently used
OPP.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>