irqdomain: Export irq_domain_free_irqs_top()

Export irq_domain_free_irqs_top(), making it usable for drivers compiled as
modules.

Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>