Eliminate duplicated & dead code.

MFC after:	3 days
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.
drm/radeon: Wake up userland after page flip

For instance, this caused issues in KDE, such as stuttered animations
(with desktop effects enabled).
mdoc: remove superfluous paragraph macro.
mdoc: add missing El.