usb: kbd: Properly translate up/down arrow keys

So far arrows key pressed on an USB keyboard got translated to some
low ASCII control sequences (Ctrl+N, Ctrl+P). Some programs understand
these codes, but the standard for those keys is to use ANSI control
sequences for cursor movement (ESC [ A).
Our own boot menu is a victim of this, currently we cannot change the
selection with an USB keyboard due to this.

Since we already implement a queue for USB key codes, we can just insert
the three character ANSI sequence into the key buffer. This fixes the
bootmenu, and is more universal for other users (UEFI) as well.

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