drm/vmwgfx: Also check for crtc status while checking for DU active

During modeset check it is possible to have all crtc_state's in atomic
state. Check for crtc enable status while checking for display unit
active status. Only error if enabling a crtc while display unit is not
active.

Cc: <stable@vger.kernel.org>
Fixes: 9da6e26c: ("drm/vmwgfx: Fix a layout race condition")
Signed-off-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>