arm64: Kconfig: Allow build irq-stm32mp-exti driver as module

Drop auto-selecting the driver, so it can be built either as a
module or built-in.
Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240620083115.204362-9-antonio.borneo@foss.st.com

arch/arm64/Kconfig.platforms

@@ -309,7 +309,6 @@ config ARCH_STM32
 	select GPIOLIB
 	select PINCTRL
 	select PINCTRL_STM32MP257
-	select STM32MP_EXTI
 	select ARM_SMC_MBOX
 	select ARM_SCMI_PROTOCOL
 	select COMMON_CLK_SCMI