mfd: ab3100: Split ab3100 headers out of abx500.h

The U8500 has its own set of separate header, so the abx500
becomes completely abstract. Do the same split for the AB3100
legacy ASIC.

Signed-off-by: Marcus Cooper <marcus.xm.cooper@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>