video: Add helpers for vidconsole for the copy framebuffer

Add a convenience function to call video_sync_copy() for a vidconsole.
Also add a memmove() helper, which does the memmove() as well as the sync.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Anatolij Gustschin <agust@denx.de>
Tested-by: Bin Meng <bmeng.cn@gmail.com>