twl4030_charger: use runtime_pm to keep usb phy active while charging.

The twl4030 usb phy needs to be active while we are using
the USB VBUS as a current source for charging.
In particular, the usb3v1 regulator must be enabled and the
PHY_PWR_PHYPWD bit must be set to keep the phy powered.

commit ab37813f
    twl4030_charger: Allow charger to control the regulator that feeds it

gave the charger control over the regulator, but didn't resolve
the PHY_PWR_PHYPWD issue.

Now that both of these are controlled by runtime_pm in
phy-twl4030-usb, we can simply take a runtime_pm reference to the USB
phy whenever the charger wants to use it as a current source.

So this patch reverts the above commit, and adds the necessary
runtime_pm calls.

Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Sebastian Reichel <sre@kernel.org>