video: Move the console commands to cmd/

Move these commands and the implementation to the cmd/ directory, which is
where most commands are kept.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
[agust: keep vidconsole_position_cursor() in vidconsole uclass]
Signed-off-by: Anatolij Gustschin <agust@denx.de>