genirq/test: Select IRQ_DOMAIN

These tests use irq_domain_alloc_descs() and so require CONFIG_IRQ_DOMAIN.

Fixes: 66067c3c ("genirq: Add kunit tests for depth counts")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: David Gow <davidgow@google.com>
Link: https://lore.kernel.org/all/20250822190140.2154646-2-briannorris@chromium.org
Closes: https://lore.kernel.org/lkml/ded44edf-eeb7-420c-b8a8-d6543b955e6e@roeck-us.net/