power: axp209: Reduce magic values by adding defines for LDO[234]

The AXP209 has a few 'magisc-ish' values that are better served with
clear defines.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
Signed-off-by: Priit Laes <plaes@plaes.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>