ARM: irq: Call irqchip_init if no init_irq function is specified

More and more sub-architectures are using only the irqchip_init
function. Make the core code call this function if no init_irq field is
provided in the machine description to remove some boilerplate code.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm/kernel/irq.c

@@ -26,6 +26,7 @@
 #include <linux/ioport.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
+#include <linux/irqchip.h>
 #include <linux/random.h>
 #include <linux/smp.h>
 #include <linux/init.h>
@@ -114,7 +115,10 @@ EXPORT_SYMBOL_GPL(set_irq_flags);
 
 void __init init_IRQ(void)
 {
-	machine_desc->init_irq();
+	if (IS_ENABLED(CONFIG_OF) && !machine_desc->init_irq)
+		irqchip_init();
+	else
+		machine_desc->init_irq();
 }
 
 #ifdef CONFIG_MULTI_IRQ_HANDLER