DA9055 GPIO driver

This is the GPIO patch for the DA9055 PMIC. This patch has got
dependency on the DA9055 MFD core.

This patch is functionally tested on SMDK6410 board.

Signed-off-by: David Dajun Chen <dchen@diasemi.com>
Signed-off-by: Ashish Jangam <ashish.jangam@kpitcummins.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>