tcx: use tcx_set_dirty() for accelerated ops

Rather than calling memory_region_set_dirty() directly, make sure that we call
tcx_set_dirty() instead. This ensures that the 24-bit plane and cplane are
also invalidated correctly.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
