dm: x86: Add a common PIRQ init function

Most x86 interrupt drivers will want to use the standard PIRQ routing and
table setup. Put this code in a common function so it can be used by those
drivers that want it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/include/asm/irq.h b/arch/x86/include/asm/irq.h
index 74da66e..46e1c31 100644
--- a/arch/x86/include/asm/irq.h
+++ b/arch/x86/include/asm/irq.h
@@ -65,4 +65,11 @@
  */
 void cpu_irq_init(void);
 
+/**
+ * irq_router_common_init() - Perform common x86 interrupt init
+ *
+ * This creates the PIRQ routing table and routes the IRQs
+ */
+int irq_router_common_init(struct udevice *dev);
+
 #endif /* _ARCH_IRQ_H_ */