irqchip/stm32-exti: Skip secure events

Secure OS can reserve some EXTI events, marking them as "secure" by setting
the corresponding bit in register SECCFGR (aka TZENR).  These events cannot
be used by Linux.

Read the list of reserved events and check it during interrupt domain
allocation.

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240415134926.1254428-6-antonio.borneo@foss.st.com