dt-bindings: pinctrl: stm32: Add missing interrupts property

Driver use interrupt-parent field so update the bindings to allow it.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200513145935.22493-15-benjamin.gaignard@st.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>