ab8500-charger: Add support for autopower on AB8505 and AB9540

Accessing autopower register fails on the AB8505 and ab9540 as
the fallback software control register has moved.

Signed-off-by: Marcus Cooper <marcus.xm.cooper@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Mattias WALLIN <mattias.wallin@stericsson.com>
Reviewed-by: Nicolas GUION <nicolas.guion@stericsson.com>
Reviewed-by: Jonas ABERG <jonas.aberg@stericsson.com>
Tested-by: Jonas ABERG <jonas.aberg@stericsson.com>