drivers/interrupt: it8xxx2: Register interrupt number 0 to handle

In the it8xxx2 chip, the interrupt for INT0 is reserved. However,in some
stress tests, the unhandled IRQ0 issue occurs. To prevent the system from
going directly into kernel panic, we implemented a workaround by
registering interrupt number 0 and doing nothing in the IRQ0 handler.
The side effect of this solution is that when IRQ0 is triggered, it will
take some time to execute the routine. There is no need to worry about
missing interrupts because each IRQ's ISR is write-clear, and if the
status is not cleared, it will continue to trigger.

Signed-off-by: Tim Lin <tim2.lin@ite.corp-partner.google.com>