MFC r257869:

drm: Initialize "handle" to 0 before calling drm_gem_handle_create()

This is variable is being checked in drm_gem_name_create() before being
set.

Approved by:	re (delphij)
MFC r257870:

drm/radeon: Wake up userland after page flip

For instance, this caused issues in KDE, such as stuttered animations
(with desktop effects enabled).

Approved by:	re (kib)