Add fdtoverlay to .gitignore

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/.gitignore b/.gitignore
index 545b899..ee4e489 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,5 +13,6 @@
 /version_gen.h
 /fdtget
 /fdtput
+/fdtoverlay
 /patches
 /.pc