pinctrl: Add IRQ related DT properties of STM32 pinctrl

Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

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

@@ -14,6 +14,9 @@ Required properies:
  - #size-cells	: The value of this property must be 1
  - ranges	: defines mapping between pin controller node (parent) to
    gpio-bank node (children).
+ - interrupt-parent: phandle of the interrupt parent to which the external
+   GPIO interrupts are forwarded to.
+ - st,syscfg: phandle of the syscfg node used for IRQ mux selection.
  - pins-are-numbered: Specify the subnodes are using numbered pinmux to
    specify pins.