systemd: add PACKAGECONFIG for xkbcommon and iptables
systemd has optional support for xkbcommon (verify keymaps when locale changes)
and iptables (configure NAT rules).
Add PACKAGECONFIG options for these, disabling iptables by default and
respecting the X11 DISTRO_FEATURE for libxkbcommon (as the code involves X11
keymaps).
Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
