video/console: Implement relative cursor movement ANSI handling

The ANSI terminal escapce sequence standard defines relative cursor
movement commands (ESC [ A-F). So far the DM_VIDEO console code was
ignoring them.

Interpret those sequences and move the cursor by the requested amount of
rows or columns in the right direction. This brings the code on par with
the legacy video console driver (cfb_console).

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Simon Glass <sjg@chromium.org>