gpio: driver for 42 AB8500 GPIO pins

To get rid of port expanders, the free GPIOs of ab8500
can be used. There are 42 GPIO pins. Out of which 16
are interrupt capable.This patch implements 16 virtual
IRQ mapped to 16 interrupt capable AB8500 GPIOs.

Signed-off-by: Bibek Basu <bibek.basu@stericsson.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
[Renamed header file as per MFD structure]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>