ABI: testing: sysfs-class-power: Adds "Long Life" entry

Adds a brief desciption of the "Long Life" charge type and adds "Long Life"
to the list of valid values.

Signed-off-by: Ricardo Rivera-Matos <rriveram@opensource.cirrus.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>