nios2: Miscellaneous header files

This patch introduces a few nios2-specific header files.

Signed-off-by: Ley Foon Tan <lftan@altera.com>
diff --git a/arch/nios2/include/asm/mutex.h b/arch/nios2/include/asm/mutex.h
new file mode 100644
index 0000000..ff6101a
--- /dev/null
+++ b/arch/nios2/include/asm/mutex.h
@@ -0,0 +1 @@
+#include <asm-generic/mutex-dec.h>