ARM: dts: axp22x.dtsi: Add reg_drivebus node

Add a node describing the drivebus regulator which is an (optional)
part of the axp221/axp223 pmic. Since this regulator may not be
available at all depending on the board, mark it as disabled by
default.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>