Enhance twl4030_charger functionality. - V2

Hi Sebastian,
here is V2 of my patches to improve the twl4030 charger. They include improved documentation and removal of changes to the CVENAC bit which I didn't properly understand.

One patch needs to make a change in drivers/mfd, and that has been acked by Lee Jones.

Summary from before:
These patches make a number of improvements to twl4030_charger.

Some are just internal cleanups (e.g. use of devres). Others allow better control of charging through both manual and automatic means.

- the maximum current can be configured via sysfs.
- the charger will only draw that current if it can do so without the voltage dropping too much
- a 'continuous' mode is available which ignores voltage and just takes what it can (to be used with caution, but very useful in some circumstances).
- 'ac' and 'usb' power sources can be configured separately.

Thanks,
NeilBrown

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NeilBrown (14):
twl4030_charger: use devm_request_threaded_irq
twl4030_charger: use devres for power_supply_register and kzalloc.
twl4030_charger: use runtime_pm to keep usb phy active while charging.
twl4030_charger: trust phy to determine when USB power is available.
twl4030_charger: split uA calculation into a function.
twl4030_charger: allow fine control of charger current.
twl4030_charger: distinguish between USB current and 'AC' current
twl4030_charger: allow max_current to be managed via sysfs.
twl4030_charger: only draw USB current as negotiated with host.
twl4030_charger: enable manual enable/disable of usb charging.
twl4030_charger: add software controlled linear charging mode.
twl4030_charger: add ac/mode to match usb/mode
twl4030_charger: Increase current carefully while watching voltage.
twl4030_charger: assume a 'charger' can supply maximum current.

 .../ABI/testing/sysfs-class-power-twl4030          |   45 ++
 drivers/mfd/twl-core.c                             |    9 
 drivers/power/twl4030_charger.c                    |  573 +++++++++++++++++---
 3 files changed, 536 insertions(+), 91 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-power-twl4030

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