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: NSaravanan Sekar <sravanhome@gmail.com>
Reviewed-by: NAndy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

Documentation/ABI/testing/sysfs-class-power-mp2629

+What:		/sys/class/power_supply/mp2629_battery/batt_impedance_compen
+Date:		April 2020
+KernelVersion:	5.7
+Description:
+		Represents a battery impedance compensation to accelerate charging.
+
+                Access: Read, Write
+                Valid values: Represented in milli-ohms. Valid range is [0, 140].