This patch adds basic support for Analog Devices I2C programmable linear
battery charger.

With this driver, some parameters can be read and configured such as:
* trickle charge current level (PRECHARGE_CURRENT)
* trickle charge voltage threshold (VOLTAGE_MIN)
* weak charge threshold (VOLTAGE_AVG)
* constant current (CONSTANT_CHARGE_CURRENT)
* constant charge voltage limit (CONSTANT_CHARGE_VOLTAGE_MAX)
* battery full (CAPACITY_LEVEL)
* input current limit (INPUT_CURRENT_LIMIT)
* charger status (STATUS)
* battery status (CAPACITY_LEVEL)
* termination current (CHARGE_TERM_CURRENT)

Datasheet:
http://www.analog.com/media/en/technical-documentation/data-sheets/ADP5061.pdfSigned-off-by: Stefan Popa <stefan.popa@analog.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>