tty: vt: define an enum for ascii characters

I didn't find definitions for ascii in the kernel yet, so define it for
non-printable characters used here.

Note we use ' ' instead of 32 on one line too.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Tested-by: Helge Deller <deller@gmx.de> # parisc STI console
Link: https://lore.kernel.org/r/20240122110401.7289-18-jirislaby@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>