BatteryService: Add support for oem fast charger detection

Based on AOSPA fw/base 0af31949c69f7c306b49ecf2c25579300973fdc9
  - https://github.com/AOSPA/android_frameworks_base/commit/0af31949c69f7c306b49ecf2c25579300973fdc9



Allows to indicate whether a device is charged using a
proprietary oem fast charge solution which writes status
to sysfs.
[nift4: Some devices turn off fast charging when display is on,
which is why even though AOSP detects the fast charger, the user won't
actually get to see it without this commit.]

The oem fast charge detection tries to be as generic as possible and is
configured via overlays.

nift4:
- port to 13
- support using custom value for path, don't hardcode 1
- big cleanup

Change-Id: Ia91a9c3bb20967c5aac18c24ac7c2be10a0b8bf1
Signed-off-by: Alexander Martinz <alex@amartinz.at>