genirq: Add preflow handler support

sparc64 needs to call a preflow handler on certain interrupts befor
calling the action chain. Integrate it into handle_fasteoi_irq. Must
be enabled via CONFIG_IRQ_FASTEOI_PREFLOW. No impact when disabled.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: David S. Miller <davem@davemloft.net>
diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
index 48ad25f..9149be7 100644
--- a/kernel/irq/Kconfig
+++ b/kernel/irq/Kconfig
@@ -35,6 +35,9 @@
 config HARDIRQS_SW_RESEND
        def_bool n
 
+config IRQ_PREFLOW_FASTEOI
+       def_bool n
+
 config SPARSE_IRQ
 	bool "Support sparse irq numbering"
 	depends on HAVE_SPARSE_IRQ