Documentation: dt: Remove ngpios from stm32-pinctrl binding

Remove "ngpios" bindings definition as it is no more used in stm32 pinctrl
driver.
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/st,stm32-pinctrl.txt

@@ -38,8 +38,6 @@ Optional properties:
  - st,syscfg: Should be phandle/offset pair. The phandle to the syscon node
    which includes IRQ mux selection register, and the offset of the IRQ mux
    selection register.
- - ngpios: Number of gpios in a bank (to use if bank gpio numbers is less
-   than 16).
  - gpio-ranges: Define a dedicated mapping between a pin-controller and
    a gpio controller. Format is <&phandle a b c> with:
 	-(phandle): phandle of pin-controller.