power: supply: bq27xxx: Add bulk transfer bus methods

Declare bus.write/read_bulk/write_bulk().
Add I2C write/read_bulk/write_bulk() to implement the above.
Add bq27xxx_write/read_block/write_block() helpers to call the above.

Signed-off-by: Matt Ranostay <matt@ranostay.consulting>
Signed-off-by: Liam Breck <kernel@networkimprov.net>
Acked-by: "Andrew F. Davis" <afd@ti.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>