devices: allow sending on device-add notifications for major/minor-less devices

This is usefull for getting device plug/unplug notifications for
things like some USB adapters which do not have major/minor
numbers.

Change-Id: I3b77f6629652d7d13e34fc9f3606260bf27dc9b6
Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Reviewed-by: Gumbel, Matthew K <matthew.k.gumbel@intel.com>
Reviewed-by: Jovanovic, Radivoje <radivoje.jovanovic@intel.com>
Reviewed-by: Boie, Andrew P <andrew.p.boie@intel.com>
Tested-by: Boie, Andrew P <andrew.p.boie@intel.com>