qcom-common: Depreciate usage of BOARD_CHARGING_MODE_BOOTING_LPM

 * Switch to using androidboot.bootchg to check for offmode charging
   This allows us to support charging on pre-kitkat and kitkat bootloaders

   Requires http://review.cyanogenmod.org/#/c/68614/

Change-Id: I33e386bf09ab3a934d32cf2ae34d23f7b95a5539