power_supply: add CHARGER_TEMP and CHARGER_TEMP_MAX properties

CHARGER_TEMP reflects the temperature of the charging chip, and
CHARGER_TEMP_MAX reflects the temperature threshold at which the
hardware will take action to reduce the temperature of the charger.

Change-Id: I9cba8e370c753ac5aa33252fce0ea446f061b4c0
Signed-off-by: Nicholas Troast <ntroast@codeaurora.org>