mfd: Parametrize ab8500 IRQ masks and registers

This makes the AB8500 state struct contain the IRQ mask and
register offsets previously hard-coded so as to make room for
more AB8500 variants.

Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@stericsson.com>
Signed-off-by: Alex Macro <alex.macro@stericsson.com>
Signed-off-by: Michel Jaouen <michel.jaouen@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>