drm/vmwgfx: Use the new event init/free functions

Cc: Rob Clark <robdclark@gmail.com
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452548477-15905-5-git-send-email-daniel.vetter@ffwll.ch


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>