Use the label to reference the pin controller node, so that we can use
sunxi-common-regulators with sunxi families that don't share the same
address space mappings, such as sun9i.

This patch is mostly space changes due to the reduction of node parents.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>