init: add detection of charging mode

-when BOARD_CHARGING_MODE_BOOTING_LPM is set to a path_to_sysfs_attribute
 then it and lpm.rc will be read accordingly.

-adapted from techomancer's original change:
 (add detection of charging mode, remove the code for parsing param.lfs,
  since it is not needed)
 http://goo.gl/I19GG

Change-Id: I64c2379225e00afaaf17ee03eab67546781668f8
Merge "init: add detection of charging mode" into alpha