mfd: ab8500-core: Add device for new RTC version for AB8540 cut2

AB8540 RTC have changed between AB8540_cut1 and AB8540_cut2.Different
ressources to define for those two version.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Julien Delacou <julien.delacou@stericsson.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>