pinctrl: qcom-spmi-gpio: Migrate to pinconf-generic

Instead of the driver caring about implementation details like device
tree, just provide information about driver specific pinconf parameters
to pinconf-generic which takes care of parsing the DT.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Tested-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>