drm/vmwgfx: Add new-style PM hooks to improve hibernation behavior

Add the new-style PM hooks prepare and complete. This allows us to
power up the device again after the hibernation image has been created, and
display output will thus be active until the VM is finally powered off.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>