metag: export metag_code_cache_flush_all

Various file systems indirectly use metag_code_cache_flush_all(), so
when they're built as modules we get build errors like the following:

ERROR: "metag_code_cache_flush_all" [fs/xfs/xfs.ko] undefined!

Therefore export this function to modules to fix the errors. This was
hit by a randconfig build.
Signed-off-by: James Hogan <james.hogan@imgtec.com>

arch/metag/mm/cache.c

@@ -460,6 +460,7 @@ void metag_code_cache_flush_all(const void *start)
 
 	metag_phys_code_cache_flush(start, 4096);
 }
+EXPORT_SYMBOL(metag_code_cache_flush_all);
 
 void metag_code_cache_flush(const void *start, int bytes)
 {