mfd: Support for the AB8500 AB8505 variant

This builds upon the changes done to support AB9540 so as
also to support the AB8505 derivative of the AB8500
circuit.

Signed-off-by: Bengt Jonsson <bengt.g.jonsson@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>