Revert "power: remove POWER_SUPPLY_PROP_CAPACITY_LEVEL"

This reverts commit 8efe444038a205e79b38b7ad03878824901849a8 and
4cbc76eadf56399cd11fb736b33c53aec9caab8c.

Richard@laptop.org was apparently using CAPACITY_LEVEL for debugging
battery/EC problems, and was upset that it was removed.  This readds it.

Conflicts:

	Documentation/power_supply_class.txt

Signed-off-by: Andres Salomon <dilinger@collabora.co.uk>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>
diff --git a/Documentation/power/power_supply_class.txt b/Documentation/power/power_supply_class.txt
index c6cd495..709d955 100644
--- a/Documentation/power/power_supply_class.txt
+++ b/Documentation/power/power_supply_class.txt
@@ -108,6 +108,8 @@
 ENERGY_FULL, ENERGY_EMPTY - same as above but for energy.
 
 CAPACITY - capacity in percents.
+CAPACITY_LEVEL - capacity level. This corresponds to
+POWER_SUPPLY_CAPACITY_LEVEL_*.
 
 TEMP - temperature of the power supply.
 TEMP_AMBIENT - ambient temperature.