package/rpm: add missing kconfig dependency to zlib

Since we build-depend on zlib, forcibly select it from kconfig.

This went unnoticed so far, because we did select openssl which
in turn selects zlib. But rpm needs zlib for itself, too.

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