power_supply: Add new lp8788 charger driver

TI LP8788 PMU supports regulators, battery charger, RTC, ADC, backlight
driver and current sinks.

This patch supports the charger operations including the charger
interrupt handling.

The LP8788 charger driver provides configurable platform data.  The
charger platform data includes ADC input ID, maximum battery voltage,
charging parameters and etc.

The ADC input is used for getting the battery voltage and temperature.
Charging parameters are used for updating the charger operations such
like setting charging current and setting End-of-charge conditions.

When the charging interrupt occurs, power supply uevents are generated
in order to update the user-space information.  For platform specific
charger action, the charger_event() function can be used in the
platform side.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>