dts: mfd: it8801: Require irq-gpios to prevent driver crashes

Marked the irq-gpios property as "required: true" in the yaml file.
This ensures that the property is always defined in the device tree,
preventing the driver from crashing when irq-gpios is missing.

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