power: supply: olpc_battery: Add OLPC XO 1.75 support

The battery and the protocol are essentially the same as OLPC XO 1.5,
but the responses from the EC are LSB first.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>