mfd: ab8500-core: Hierarchical interrupt registers

Make use of the hierarchical interrupt rergister called
ITLatchHier1 - 3 also for the 8500 platform (currently the
hierarchical interrupt registers are used only for the 8540
and 9540 platforms). This will make the interrupt routing
go faster since fewer i2c reads need to made in the most
common cases.

Signed-off-by: Dariusz Szymczak <dariusz.xd.szymczak@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Mian Yousaf KAUKAB <mian.yousaf.kaukab@stericsson.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>