vmwgfx: Switch to VGA when we drop master and vmwgfx fbdev is not active

Previously this was not done when any 3D resource was active,
since that meant disabling the fifo with all 3D state lost.
Now, if there are still 3D resources active, we use the svga hide feature.

This fixes X server VT switching with 3D enabled.

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