power_supply: Add cold to the POWER_SUPPLY_HEALTH report values

Some systems are able to report problems with batteries being under
temperature.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Anton Vorontsov <cbouatmailru@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>