microblaze: Declare microblaze_kgdb_break in header

This patch removes the warning:
arch/microblaze/kernel/kgdb.c:81:6: warning: no previous prototype for
'microblaze_kgdb_break' [-Wmissing-prototypes]

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/include/asm/kgdb.h

@@ -23,6 +23,9 @@ static inline void arch_kgdb_breakpoint(void)
 	__asm__ __volatile__("brki r16, 0x18;");
 }
 
+struct pt_regs;
+asmlinkage void microblaze_kgdb_break(struct pt_regs *regs);
+
 #endif /* __ASSEMBLY__ */
 #endif /* __MICROBLAZE_KGDB_H__ */
 #endif /* __KERNEL__ */