um: Remove IRQ_NONE type

We don't actually use this in um_request_irq(), so it can
never be assigned. It's also not clear what that would be
useful for, so just remove it.

This results in quite a number of cleanups, all the way to
removing the "SIGIO on close" startup check, since the data
it assigns (pty_close_sigio) is not used anymore.

While at it, also make this an enum so we get a minimum of
type checking, and remove the IRQ_NONE hack in virtio since
we now no longer have the name twice.

Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/include/shared/irq_user.h b/arch/um/include/shared/irq_user.h
index 5e975a9..07239e8 100644
--- a/arch/um/include/shared/irq_user.h
+++ b/arch/um/include/shared/irq_user.h
@@ -9,10 +9,11 @@
 #include <sysdep/ptrace.h>
 #include <stdbool.h>
 
-#define IRQ_READ  0
-#define IRQ_WRITE 1
-#define IRQ_NONE 2
-#define NUM_IRQ_TYPES (IRQ_NONE + 1)
+enum um_irq_type {
+	IRQ_READ,
+	IRQ_WRITE,
+	NUM_IRQ_TYPES,
+};
 
 struct siginfo;
 extern void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs);