package/busybox: update licensing info

Busybox is mainly licensed under the GPL-2.0, but the bzip2 part is a
modified copy of the bzip2/libbzip2 project, which comes with its own
license.

Update the licensing information accordingly.

Add the hash for the new license file, and fixup indentation (2 spaces).

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>