ARM: dts: sunxi: Fix OPP arrays

Even though it translates to the same thing down to the binary level, we
should have an array of 2 number cells to describe each OPP, which in
turns create a validation warning.

Let's fix this.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20210901091852.479202-42-maxime@cerno.tech