gitignore: Add defconfig and fdtgrep

Ignore defconfig and tools/fdtgrep.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/.gitignore b/.gitignore
index a40c277..33abbd3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -48,6 +48,7 @@
 /LOG
 /spl/
 /tpl/
+/defconfig
 
 #
 # Generated include files