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 we should enter offline charging mode

Change-Id: I2b073a0968d65ba9e3bf6b397280241c1fb0c0f9