power: add driver for battery reading on iPaq h3xxx

This adds a driver for reading the battery status of the
battery connected to the Atmel microcontroller on the
iPAQ h3xxx series.

Based on a driver from handhelds.org 2.6.21 kernel, written
by Alessandro GARDICH.

Signed-off-by: Dmitry Artamonow <mad_soft@inbox.ru>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>