power_supply: Support for Texas Instruments BQ27200 battery managers

These battery managers came in two different packages: one for I2C
busses (BQ27200) and one for HDQ busses (BQ27000).

This driver currently supports only the I2C chip version but the code
is designed in order to easily allow the HDQ chip version integration.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: make things static, use kasprintf()]
Signed-off-by: Rodolfo Giometti <giometti@linux.it>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>