pxa: magician/hx4700: Convert to gpio-regulator from bq24022

The bq24022 on these machines is a very simple regulator using gpios.
One provides the on/off functionality and a second one is used to
change the current between 100 and 500 mA.

This functionality can also be provided by the more generic gpio-regulator.

Therefore convert both machines which makes it possible to remove the
bq24022 driver later on.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Paul Parsons <lost.distance@yahoo.com>
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>