powerpc/boot: Ignore .dtb files.

Signed-off-by: NIan Campbell <ian.campbell@citrix.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/boot/.gitignore

@@ -16,6 +16,7 @@ mktree
 uImage
 cuImage.*
 dtbImage.*
+*.dtb
 treeImage.*
 zImage
 zImage.initrd