xtensa: move built-in PIC to drivers/irqchip

Extract xtensa built-in interrupt controller implementation from
xtensa/kernel/irq.c and move it to other irqchips, providing way to
instantiate it from the device tree.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>
diff --git a/include/linux/irqchip/xtensa-pic.h b/include/linux/irqchip/xtensa-pic.h
new file mode 100644
index 0000000..48718ae
--- /dev/null
+++ b/include/linux/irqchip/xtensa-pic.h
@@ -0,0 +1,18 @@
+/*
+ * Xtensa built-in interrupt controller
+ *
+ * Copyright (C) 2002 - 2013 Tensilica, Inc.
+ * Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#ifndef __LINUX_IRQCHIP_XTENSA_PIC_H
+#define __LINUX_IRQCHIP_XTENSA_PIC_H
+
+struct device_node;
+int xtensa_pic_init_legacy(struct device_node *interrupt_parent);
+
+#endif /* __LINUX_IRQCHIP_XTENSA_PIC_H */