power: supply: mp2629: Add impedance compensation config

Allows the user to compensate the intrinsic resistance of the battery
to accelerate the charging cycle.

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>