ARM: devicetree: Add .dtb files to arch/arm/boot/.gitignore

Compiled device tree blobs shouldn't be committed in the kernel
tree, so ideally git should ignore them.

This patch will enable ignoring of any .dtb files which appear in
arch/arm/boot/

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/arch/arm/boot/.gitignore b/arch/arm/boot/.gitignore
index ce1c5ff..3c79f85 100644
--- a/arch/arm/boot/.gitignore
+++ b/arch/arm/boot/.gitignore
@@ -3,3 +3,4 @@
 xipImage
 bootpImage
 uImage
+*.dtb