charger: Draw battery percentage over charger screen

Let user know the exact battery capacity.

Change-Id: Ie2abaeee0e443cd2a730780488287ad4d9ea1e9a
charger: Toggle backlight while in charger mode.

The backlight is now toggled on/off in the charger mode via a sysfs
node. This is to compensate for the fact that on certain targets the
FBIOBLANK ioctl does not turn off the backlight.

Change-Id: I7c4531e7f1b0599b9a1f5ed6f95d13ee6a664066
CRs-fixed: 514940
charger: support alarm in power off charging

To implement this feature need to let the phone reboot some time
earlier than the alarm time.

CRs-fixed: 540039
Change-Id: I5001631114994f5bc29313bbd52395c43f7c4810