u8800: Update charge/discharge voltage mapping (WIP).

Adjusted charging voltage as it goes greatly up. Just assume 50% as 0% for now.
Discharge mappings are adjusted to get better smoothness. Since drop from 3.5V
to 3.4V is quick, just assume 0% as 3.4V and 1% as above.

Change-Id: I417d8885a9d6b0ce62ba642bf808031e6a4ba199