ARM: dts: sun8i-r40: Add "cpu-supply" node for sun8i-r40 based board

The CPU of sun8i-r40 is powered by PMIC, let's add "cpu-supply" node.

Signed-off-by: qianfan Zhao <qianfanguijin@163.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Tested-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20220517013607.2252-2-qianfanguijin@163.com