power: supply: bq27xxx: Add chip data memory read/write support

Add these to enable read/write of chip data memory RAM/NVM/flash:
  bq27xxx_battery_seal()
  bq27xxx_battery_unseal()
  bq27xxx_battery_set_cfgupdate()
  bq27xxx_battery_soft_reset()
  bq27xxx_battery_read_dm_block()
  bq27xxx_battery_write_dm_block()
  bq27xxx_battery_checksum_dm_block()

Signed-off-by: Matt Ranostay <matt@ranostay.consulting>
Signed-off-by: Liam Breck <kernel@networkimprov.net>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>