lxdm: update to latest sources and fixes

* /etc/lxdm/lxdm.conf was empty since out of tree build causing greeter not started
* pam is now an option to configure - set it based upon distro feature
* bash was added to RDEPENDS - it is required by /etc/lxdm/Xsession

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>