power_supply: bq27x00: add BQ27500 support

BQ27500 is newer fuel gauge chip from TI with slightly changed
register layout and some different register semantics. Add new i2c
ID for it and handle differences where needed. Also rename bq27200
functions to bq27x00, as they are no longer bq27200 specific.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Acked-by: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>