power_supply: Add constant charge_current and charge_voltage properties

Constant Charge Current(CC) is charging parameter which limit the
maximum current which can be pumped into the battery during charge cycle.

Constant Charge Voltage(CV) is also charging parameter which limit the
maximum voltage that battery can reach during charge cycle.

It is very common practice that at low or high temperatures we
do not charge the batteries upto it's fullest charge voltage
to avoid battery and user safety issues.

These sysfs properties will be useful for debug and to implement
certain user space policies like "Charging limited due to OverTemp".

Signed-off-by: Ramakrishna Pallala <ramakrishna.pallala@intel.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>

Documentation/power/power_supply_class.txt

@@ -112,6 +112,10 @@ CHARGE_COUNTER - the current charge counter (in µAh).  This could easily
 be negative; there is no empty or full value.  It is only useful for
 relative, time-based measurements.
 
+CONSTANT_CHARGE_CURRENT - constant charge current programmed by charger.
+
+CONSTANT_CHARGE_VOLTAGE - constant charge voltage programmed by charger.
+
 ENERGY_FULL, ENERGY_EMPTY - same as above but for energy.
 
 CAPACITY - capacity in percents.