arm64: dts: st: Add interrupt parent to pinctrl on stm32mp251

Add exti1 as interrupt parent for the two pin controllers.  Add the
additional required property st,syscfg.

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240415134926.1254428-12-antonio.borneo@foss.st.com