ARM: dts: stm32: Set gpio controller as interrupt controller on F4 and F7

This patch set each gpio controller as a interrupt controller. User who
wants to use gpio as interrupt will have choice to use either "gpiolib"
interface or "common" interrupt interface.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>