regulator: pfuze: provide power over standby handler ...

This patch is providing an optional power off handler
which will configure standby state of the PMIC to disable all power lines.

In my power consumption test on RIoTBoard, I got the following results:
power off without this patch:   320 mA
power off with this patch:      2   mA

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

regulator: Add pfuze driver ...

This is not yet a regulator driver, only the register map is
exported as /dev/pfuze* so the registers can be accessed for
debugging purposes.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>