ARM: dts: sun8i: a23/a33: Fix OPP DTC warnings

DTC will emit a warning on our OPPs nodes for the common DTSI between the
A23 and A33 since those nodes use the frequency as unit addresses, but
don't have a matching reg property.

Fix this by moving the frequency to the node name instead.

Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>