genirq: Add internal state field to irq_desc

That field will contain internal state information which is not going
to be exposed to anything outside the core code - except via accessor
functions. I'm tired of everyone fiddling in irq_desc.status.

core_internal_state__do_not_mess_with_it is clear enough, annoying to
type and easy to grep for. Offenders will be tracked down and slapped
with stinking trouts.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/internals.h

@@ -1,5 +1,9 @@
 /*
  * IRQ subsystem internal functions and variables:
+ *
+ * Do not ever include this file from anything else than
+ * kernel/irq/. Do not even think about using any information outside
+ * of this file for your non core code.
  */
 #include <linux/irqdesc.h>
 
@@ -9,6 +13,8 @@
 # define IRQ_BITMAP_BITS	NR_IRQS
 #endif
 
+#define istate core_internal_state__do_not_mess_with_it
+
 extern int noirqdebug;
 
 /*