healthd: charger: Add board overrides in mode_charger

Add following overrides in mode_charger to improve the off-mode charging
user experience:
 1. Draw battery information on the animation, such as: capacity;
 2. Handle board specific battery status update;
 3. Handle board specific mode charger initialization;
 4. Turn on/off the backlight explicitely;
 5. Reduce the unplugged shutdown delay to 1 seccond;
 6. Do a period chorse and then heartbeat to reduce the animation boot
time.

Change-Id: Ic2b7ab6deeb52c4effe3b4af9b590950d5ee97f1