mainboard/apple: add license headers

Change-Id: Id9487212411e5c237d26eb4e5663135f7d0720d1
Signed-off-by: Noah Glovsky <noah.glovsky@watershedschool.org>
Reviewed-on: https://review.coreboot.org/14425
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
diff --git a/src/mainboard/apple/macbookair4_2/romstage.c b/src/mainboard/apple/macbookair4_2/romstage.c
index f1839f0..78049bb 100644
--- a/src/mainboard/apple/macbookair4_2/romstage.c
+++ b/src/mainboard/apple/macbookair4_2/romstage.c
@@ -1 +1,2 @@
+/* No license required */
 /* dummy file */