packages: use new $($PKG)_DL_DIR) variable

packages: use new $($PKG)_DL_DIR) variable

Instead of DL_DIR, the package should now use $(PKG)_DL_DIR to ease the
transition into a new directory structure for DL_DIR.

This commit has been generated with the following scripts:

for i in $(find . -iname "*.mk"); do
	if ! grep -q "\$(DL_DIR)" ${i}; then
		continue
	fi
	pkg_name="$(basename $(dirname ${i}))"
	[ "${pkg_name}" = "package" ] && continue
	raw_pkg_name=$(echo ${pkg_name} | tr [a-z] [A-Z] | tr '-' '_')
	pkg_dl_dir="${raw_pkg_name}_DL_DIR"
	sed -i "s/\$(DL_DIR)/\$($pkg_dl_dir)/" ${i}
done

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>