irqchip/mips-gic: Directly include linux/irqdomain.h

This drivers currently obtains linux/irqdomain.h by luck and
a chain of bizarre inclusions, which we're about to fix.

Let's include the required file directly.
Signed-off-by: Marc Zyngier <maz@kernel.org>

drivers/irqchip/irq-mips-gic.c

@@ -16,6 +16,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/irqchip.h>
+#include <linux/irqdomain.h>
 #include <linux/of_address.h>
 #include <linux/percpu.h>
 #include <linux/sched.h>