buildroot

package: share downloaded files for big packages

Theses packages are given as an example of the use of the *_DL_SUBDIR feature.
There maybe other packages that would benefit from that feature, they
would need to be added on a case by case basis.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>