buildroot

support/download: make sure the download folder is created

At the moment, it means that we make sure that BR2_DL_DIR is created, in
the future, it will make sure that BR2_DL_DIR/PKG_NAME/ is created.

[Peter: drop trailing / on mkdir]
Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>