Switch remaining drivers over to drm_exec

[Christian König]

Hi guys,

switching the remaining driver over to drm_exec, cleaning up XE and the
finally remove ttm_execbug_util since it isn't used any more.

When I originally posted the patch set for drm_exec vmwgfx was to
complicated to trivially switch over. This is now done with this patch
set.

Additional to that radeon and QXL were never pushed because I couldn't
get an rb for them.

Please review and/or comment,
Christian.