Various temporary files used when building DTB files were not suffixed with
.tmp and therefore were not cleaned up by "make clean".

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Grant Likely <grant.likely@linaro.org>