init: define BOARD_CHARGING_CMDLINE parameters

Change-Id: I722e49e2a13418bf887c361c85e9d102168ca973
init: Allow load of lpm.rc by parsing a cmdline argument

A usage example could be:
BOARD_LPM_BOOT_ARGUMENT_NAME := lpm_boot
BOARD_LPM_BOOT_ARGUMENT_VALUE := 1

Where lpm_boot is the argument to read, and 1 the value of it when kernel says when should enter offline charging mode

Change-Id: I413ac98138547cca62f20e3dce3964fcd30ad483