BugLink: http://bugs.launchpad.net/bugs/1546572

To avoid users accessing them before the module has finished
initializing them and make sure they are only created if
dpm has properly initialized.
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 898b1dea)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>