Update the binding and driver for pm8994-gpio devices.

Cc: <devicetree@vger.kernel.org>
Cc: "Ivan T. Ivanov" <iivanov@mm-sol.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Björn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>