modules.d: Add a module for handling additional depmod kernel module directories

modules.d: Add a module for handling additional depmod kernel module directories

It parses depmod configuration and scans modules.dep for kernel modules
present in directories supplied in "overrides", "external", and "search"
depmod configuration options.  The resulting list of (absolute) kernel
module paths is then supplied to instmods.

* modules.d/90kernel-modules-extra/module-setup.sh: New file.
* dracut.spec (%files): Add
%{dracutlibdir}/modules.d/90kernel-modules-extra.

Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>