gpio: it8xxx2: disable irq before configuring pin interrupt

Fixed the following assertion causing by high level functions
enable gpio interrupt at the same pin at least two times:

ASSERTION FAIL [!arch_irq_is_enabled(irq)]
@ ZEPHYR_BASE/arch/common/sw_isr_common.c:84 IRQ xxx is enabled

Signed-off-by: Dino Li <Dino.Li@ite.com.tw>