drm/vmwgfx: Switch over to internal atomic API for SOU and LDU

Switch over to internal atomic API.  This completes the atomic
internal atomic switch for all the Display Units.

Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>