microblaze: Add missing export symbols for lib functions

Adding missing export symbols for loadable modules.

Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/lib/muldi3.c b/arch/microblaze/lib/muldi3.c
index d4860e1..0585bcc 100644
--- a/arch/microblaze/lib/muldi3.c
+++ b/arch/microblaze/lib/muldi3.c
@@ -58,3 +58,4 @@
 
 	return w.ll;
 }
+EXPORT_SYMBOL(__muldi3);