power: supply: Add support for mps mp2629 battery charger

The mp2629 provides switching-mode battery charge management for
single-cell Li-ion or Li-polymer battery. Driver supports the
access/control input source and battery charging parameters.

Signed-off-by: Saravanan Sekar <sravanhome@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>