power: supply: ab8500: Drop abx500 concept

Drop the entire idea with abx500 being abstract and different from ab8500
in the AB8500 charging drivers. This rids the two identical definitions
of a slew of structs in ab8500-bm.h and makes things less confusion and
easier to understand.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>