fwupd: split daemon again

In 1.3.5, fwupdprivate library was made into a shared fwupdplugin library.
This library is considered semi-private and is used by fwupd daemon and
fwupd plug-ins and now possibly third party plug-ins.

The fwupdplugin library refers to the plug-in directory in fwupd.out
causing a dependency cycle. For that reason we need to move it to out.