microblaze: Add support from PREEMPT

This patch add core PREEMPT support for Microblaze.
I tried to trace it via tracers and I was able to see any output.

I also added low level debug functions to see if that code is called.

Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/include/asm/tlbflush.h b/arch/microblaze/include/asm/tlbflush.h
index 10ec70c..bcb8b41 100644
--- a/arch/microblaze/include/asm/tlbflush.h
+++ b/arch/microblaze/include/asm/tlbflush.h
@@ -23,7 +23,7 @@
 extern void _tlbie(unsigned long address);
 extern void _tlbia(void);
 
-#define __tlbia()	_tlbia()
+#define __tlbia()	{ preempt_disable(); _tlbia(); preempt_enable(); }
 
 static inline void local_flush_tlb_all(void)
 	{ __tlbia(); }