watchdog/octeon-wdt: 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/watchdog/octeon-wdt-main.c

@@ -54,6 +54,7 @@
 #include <linux/delay.h>
 #include <linux/cpu.h>
 #include <linux/irq.h>
+#include <linux/irqdomain.h>
 
 #include <asm/mipsregs.h>
 #include <asm/uasm.h>