microblaze: Add missing headers caused by disintegration asm/system.h

It should be the part of patch
"Disintegrate asm/system.h for Microblaze"
(sha1: c40d04df152a1111c5bbcb632278394dabd2b73d)

Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/include/asm/cmpxchg.h b/arch/microblaze/include/asm/cmpxchg.h
index 0094859a..538afc0 100644
--- a/arch/microblaze/include/asm/cmpxchg.h
+++ b/arch/microblaze/include/asm/cmpxchg.h
@@ -1,6 +1,8 @@
 #ifndef _ASM_MICROBLAZE_CMPXCHG_H
 #define _ASM_MICROBLAZE_CMPXCHG_H
 
+#include <linux/irqflags.h>
+
 void __bad_xchg(volatile void *ptr, int size);
 
 static inline unsigned long __xchg(unsigned long x, volatile void *ptr,